Welcome to the forum :D
O_O 76 to 60 is a huuuuuuge drop. You have to remember that their external temperatures are the same as their internal temps. They need temps around 78-80* F, so that's an insane drop.
IMO, the 2.5 is probably better for him, but if not and you think the 1 gallon is okay remember you just need to keep it heated. You'll have to do 100% water changes every other day in the 1 gallon. A2.5 gallon needs 2 50% and one 100% water changes a week. The salt is completely uncessary. If you are worried that the decor (I doubt it is ) is the problem, just rinse well in hot water before adding again.