It's a great idea - you know he's into it, will probably soon have a dedicated room for it, and doesn't have it yet.

I like these cushions - they are firm but soft enough to be comfy: link

And this kind of stool is great with a cushion or two on top: Link

Add in a Tibetan singing bowl and some agarwood incense and you've got an amazing gift. That's a bit much for a small gift but would be a great kit.