Heh, it seems you're not alone in this goal. I have also been trying to think of a place that exists only in my dreams, as a sort of constant factor in there. For me, I've tried to create an infinite forest or wild environment on a whole other plane of existence. I'm letting my dream loose on this one, though, as I'm only intending to create a couple of general rules for it instead of really specific things. Things like:

- It's always sunny and bright.
- It is mostly a forest, but there's all kinds of other areas too.
- The environment is lively, with a lot of plants and animals.
- A couple of dream characters live in the forest and can always be found there.
etc.

Rules like those make for a predictable environment that your dream still has enough room to play with. My dream could easily plant a tower in the middle of this forest if it wanted to. I could also end up in an open field near the sea. The important thing is to set the tone of the place, not exactly how it's going to look like. Some rules you could use could be:

- There's always at least one desk, cupboard and bed in my home base.
- The dominant color in my home base is blue.
- My home base is not accessible to any dream characters, I'm always there alone.
- My home base is peaceful; I can think without being disturbed there, by anything.
etc.

Then let your mind fill in the details of what your home base exactly looks like. Maybe if you give your dream a little room it will be a lot more cooperative.