Can you put the cot in your room as a side cart to your bed? you may be able to feed bub laying down, with her in the cot, and then move away into your space.
I did this for a while, but DS was too much of a restless sleeper and would wake more often when he'd bang himself on the cot.

Can you try sharing a big mattress on the floor with bub - that way there is more room for you.
This is what I ended up doing and it worked the best. DS couldn't fall out of bed, well he could but it wouldn't hurt him. DS and I moved into his room with 2 single mattresses on the floor. I still had some back pain but not as bad as 3 in the bed. We've just recently moved a double bed in. The gap in the mattresses if they came apart a bit was making me sleep funny too and getting sore.

I still get a bit of a sore back sometimes but not as bad or as often as before.