He’s also mentioned that he feels less pressure with the doll.

Well, sure. I imagine he talks to the doll confident that it will never talk back or give him a cross look.

realistic vagina and buttocks. mouth, too?

I mean, it's like getting a fleshlight, but, with enough 'body' to start feeling like its a real person (albeit enormously more expensive).

Does he buy it clothes, and wigs, and makeup for it? Does he have tea parties with it? Just curious.

I would like to come up with ways in which I could make him feel less pressure.

You mention being into kink -- how about his tying you up and gagging you? That ought to reduce his feeling 'pressure'.