Of course you're upset - it shows you're a caring pet owner who deserves fish, and a human being.
It would be abnormal not to be.
And believe me, no other group of people could better understand, or feel more sympathy for, your pain.
Normal house bleach is fine, (but try to avoid a weird, new, clingy, concentrated kind - or anything with any fabric treatment - we once got by mistake, which is much harder on skin but doesn't seem to behave in the way regular bleach does, so I'm even not sure if dechlor works on it) and I'd let the tank soak for at least a few hours prior to a very thorough rinsing and dechlor, as any whiff of bleach can be deadly to fish.
The odds are that any bleach residue would be long gone before you're ready to even think about getting any fish, with merely a good rinse and dry used, so perhaps someone else can advise, but I use mass quantities of Prime in such cases as this, so I'll make my suggestions, and see what others say as well.
Don't forget to wipe with bleach - and rinse/wipe and dechlor - all nooks and crannies in and around the tank, including the rim and hood, although the outside could probably be done with vinegar.
You're dealing with a contagious disease, and there may have been others present you don't know about - might as well make as fresh a start as possible, with all bleach-killable bacteria/fungus gone.
Don't 'boil' your heater; I'd try to rig it, if possible, so that the part which was in water is soaked for a few hours in bleach solution, wipe it down well all over with bleach, let it dry and rinse - as a paranoid, I'd pour Prime over and rub it well around with a bit of paper towel - but try not to soak any rubber/plastic grips in bleach for too long or they'll lose their 'stick'.
They should be the first area carefully rinsed and dechlored, to inactivate the bleach.
I keep a bucket of bleach solution handy - something like that can be used to soak rocks/ornaments and soakable filter bits, (I'd do those overnight) and, of course, everything needs rinsing after.
A bucket of dechlor solution and an overnight soak in there as well - with the same treatment for the gravel, which needs a VERY thorough rinse in a bucket under running water (I'm lucky enough to have the use of a large laundry sink), working and swishing it around AFTER rinsing the bleach out of it - this will be easier in smaller quantities, if enough buckets are available - and soak in dechlor solution.
(Make sure you have hand lotion - bleach is murder on human skin as well as to germs.)
If you haven't many buckets, I suggest you try collecting any non-chemical-exposed plastic ice cream or other pails you can - they are very handy.
The impeller well can be reasonably well sterilized with Q-Tips dipped in bleach solution, used to clean it out as throroughly as possible, and rinsed as well as possible.
I actually pour a bit of Prime on Q-tips and in the well at the end of the process, and rub this all over the inside and edges of the impeller well.
But bleach around fish scares the heck out of me, and if anyone had told me prior I'd ever use it on anything fish-related, I'd have thought they were nuts.
Your filter bacteria is dead of starvation anyway - nothing will survive but disease and other organisms you won't want near your new fish, when you get him, never mind breeding a steady supply of disease and/or toxins in your filter to continually circulate through his water.
You'll need to get new media and you'll have to recycle or see if anyone from the forum is near enough, and willing and able to let you have some.
Although many people do use media from an LFS to start a tank, personally, I've bought too many fish with too many diseases to ever do that myself, but, as stated, I'm a paranoid, so it's your call.
All this is a pain, especially at a time of mourning, but it's a good deal better than getting a beautiful new fish and possibly subjecting him to the same ordeal your poor little boy failed to survive.
And perhaps someone else will come in with a better suggestion.
I'm dealing with a horrible black fungus myself - from an LFS - right now, and for quite a while previously (while I initially thought the bent bodies and other symptoms the result of injuries from a rough capture) with fish suffering from/exposed to a mycobacterial infection - from an LFS - in another tank, and my daily routine involves a lot of care in avoiding cross-contamination, although bleach apparently doesn't kill the mycobacterium and a strong solution of rubbing alchohol should be used.
I also lost two beautiful betta sororities - bought from an LFS - within months of purchase, to two different types of nematodes, after battling multiple secondary illnesses starting immediately on arrival.
This affects my perspective, and therefore my advice, something we both should bear in mind.