...using a soft wet warm cloth to "refresh" him and simultaneously arouse him by stroking his whole body...

Yeah, I'm gonna go ahead and have to make that a thing now...

I love these ideas, you have a very lucky guy on (in?) your hands to have such a caring, giving submissive at his feet!

I think there is a lot of wonderful room in a healthy dynamic for such gestures. Things that say "thank you" or "I'm yours" or even take on the angle of "you take such wonderful care of me, let me take care of you for a few minutes". I would imagine your attention alone is already serving much of that purpose, being so focused and singularly devoting your entire self to him surely has a profound effect.

Past that, brainstorming, I don't think you'll go wrong with snack delivery services and cuddles. Does he like to talk afterwards? Just lie there and bask quietly and not have to think? Get up and clean off and go do something completely different? Can you find a way to work yourself into that instinct and be a part of where it naturally wants to go? It's not often talked about, but aftercare can most definitely be for doms too! Something as small as cuddling up and whispering in his ear how amazing that just was and how lucky you are to have him and how happy he makes you would put any guy on the moon. I think it's less to do with any specific action or behavior as it is the intention and gesture from where it comes within you.