I have plants that grow attached to decor and floating plants rather than those that grow rooted in the substrate. If you want to try the kind that attach to decor, look at java fern, anubias and bucephalandra - there are different varieties of java fern and several species of anubias and buce. My floating plants are water sprite and frogbit. All of these get their fertiliser from the water so I use Seachem Flourish Comprehensive supplement for the Planted Aquarium; TNC Lite (not Complete) is another good fertiliser.
If you want plants that grow in the substrate, some need root fertiliser - Seachem Flourish root tabs is one of the best - but I know little about this type of plant. It is this type that I would plant at the same time as changing to sand. The plants grown on decor and floating plants can be added at any time, though floaters are very good at taking up ammonia and will prevent the possibility of a mini cycle.