I think you're looking for lucid dreaming, not a tulpa. From what I've gathered, a tulpa is it's own person, and you cannot create a tulpa wanting it to be somebody else, apparently forcing them to be someone they're not stresses them out (I guess? I dunno much about them other than this)
So in reality, while they're often associated, a tulpa and waifuism have almost nothing to do with each other.
If I were you, I'd search the internet on lucid dreaming, there are thousands of resources that can teach you how to lucid dream, so you can see your waifu in your dreams easily like you mentioned
Good luck!