Thanks for the good advice about putting him in a shallower tank. As long as he can make it back up into his floating Wisteria (great hammock for old fish, or any fish) I'll leave him. But I've got a place for him if he gets weaker.
I've been splitting his pellets and pushing them almost right into his mouth, so his eating has improved.
My first fish, he taught me about Betta-keeping. Bounced back from the many mistakes I made. Made me smile a lot. Still does, in fact.