Speaking as Not An Expert, only from my own experiences, reading and from what I recall generally of hours of internet searching:
I'd go for live plants, myself.
The more live plants, the healthier the tank and inhabitants, overall.
Plants, of course, process fish wastes, and sufficient plant mass (varying with type, things like duckweed and fast-growing stem plants being ideal for this) can, naturally in all senses, suck up ammonia prior to any levels appearing which could be deleterious to fish.
They foster organisms which many fish can nutritiously snack on, provide cover and plenty of scope for that favorite (in most cases) betta activity of swimming through and between things.
Although top-floaters such as duckweed must, of course, be monitored as it's so essential for bettas to have clear surface areas at which to breathe.
And a well-planted tank is much 'bigger' and full of gradually altering interest for fish...
I don't know about the current crop of posters, but the people who used to be regularly here typically fed peas weekly - most betas love them and it makes a nice change in diet, too.
Many people swear by weekly pea-feeds, as a preventative for constipation in betas.
I've never done the weekly one-day fast thing, just gave bettas in separate tanks pea-only feeds once a week, although this doesn't always work well in a community tank where a variety of foods may be given.
They do tend to preferentially go for the peas, though, at least mine always did, as long as we had good peas, but mine now tend to go extended periods without pea feeds as the frozen we've been getting are so often slimy and un-pea-like that I won't eat them or give them to my fish, unless we get organic, which are good ones.
And I still haven't noticed any constipation/bloating-type problems, except on (other) bettas which arrived with problems and were found to have either intestinal or encysted worms.
I'm rotten at remembering dates, but I believe I've had two of my current bettas (the first two males I'd ever acquired) about 3 years, and another I think about a year and a half or more, the others I have now being more recent.
So this isn't a short-term observation.
But I bought two stunted rescue bettas last year because they were sick, had them about 9 months before losing them to encysted parasites, managed to get hold of some Prazi which saved the less damaged of two surviving Giant Otos which were also exposed by having been in a tank one of those - then apparently healthy - bettas had been in, and later purchased one more stunted Betta from the same place and in size and appearance almost certainly of the same provenance as the others.
A Prazi (bath-type wormer) treatment (and some others for the obvious problems he arrived with) resulted in a healthy, beautiful - and growing, unlike the other two - male Crowntail, and if I'd been able to get hold of that type of treatment (don't think it's sold in Canada any more, I got it by luck) I could have saved all of the others, if I'd given a precautionary treatment.
In great part, the safety of such meds depends on the 'medication'.
There are some garlic-based foods that will help with, if not eliminate parasites, and the average betta almost certainly has some of probably several types.
Those foods would be not only harmless but beneficial in more than one respect.
Those chemical meds that are (I believe) less harsh types, such as the Jungle medicated food and the Gel-Tech wormer, (none of my fish recognised the latter as food - I had to saturate flake in it and hope they got enough wolfing that down, but not everyone will eat the Jungle pellets, either) are often suggested as a precautionary measure, although I actually wouldn't use anything like that without some indication of a problem.
But if certain persistent tummy issues arise, and it's not a question of impaction from a dry diet, of too-cool temperatures slowing body processes, or problems universal among animals kept forcibly inactive, (whether horses cooped up in a stall or bettas which have been kept in a small container without exercise or even the ability to move freely and stimulate natural elimination) there are a number of possible issues, of which internal parasites form one probability.
Internal infections are another, although often, apparently, such issues go hand in hand...
If I hadn't learnt to keep fish bodies in a disposable glass of water to see nematodes which had left after death or parasites actually digging/eating their way out of the corpses, and if I hadn't followed advice in emptying the gravel out of what was luckily not a Wadstad tank to see on the bare and daily siphoned-clean glass bottom what must have been hundreds of worms passed by a sorority of female betas and guppies fed Gel-Tech, I would never have seen and understood the problems causing secondary illnesses, symptoms and deaths.
My experiences have made me very aware of the prevalence of parasites in aquarium fish, and a male betta having been kept in isolation in the store from which he was purchased is no guarantee of any illness not being present.
But if you're in Britain, the same meds may not be available there as here, and many of the more effective yet safe meds have apparently been taken off the market in multiple countries, or made by prescription only.
The same level of parasitism in pet fish may not be common there, either, owing to the tighter import regulations.
I'd say talk to Wilder, myself...
Although if he's had more than one recurrence of tummy bloat, I would definitely try a wormer food, if at all possible in a bare-bottomed tank with floating plants only.