Sarahkka

I have a long undershirt with a built-in bra shelf. My boobs are reaching nutty proportions, as well, so that has made me a lot more comfy at night. I can't sleep in a bra. They drive me crazy.
The undershirt is pretty form-fitting, so it doesn't twist around or feel restrictive. Something like that might help?
Sympathy from a fellow boobasaurus!

PeanutBean

In the early days when my boobs were more sensitive than anything else on earth can be I wore a support vest to bed but then I got sweaty boobs and they started getting spotty!! So I just put up with the pain in the end! Stupid big boobs...

cuddles314

Mothercare do some really nice soft sleep bras, maybe they would help. It might take some getting used to if you normally sleep in the nuddy, but at least it'd keep them in one place for you hun. Hope you manage to get some decent sleep soon.
xx