Make sure the betta isn't bloated, not pineconing, and its eyes are not overly large. Also at least some activity is a good sign.
Also a good environment for them (heated tank that is cleaned often, accordingly based on size) will prevent you from making the betta sick.
Good luck, I'm sorry about your guy's passing.
“Some people talk to animals. Not many listen though. That's the problem.”
― A.A. Milne
Espeon female halfmoon / 10G
Jolteon male dumbo plakat / 10G