Ah - the fit ball! I remember that! DS used to love it too.

OK - you know what, it sounds like you really have made some good progress. This is a phase. It WILL pass. Getting upset and frustrated will make it last longer. I know cause I too have been there.
Sometimes we are our own worst enemies. I had a revelation at around 7.5 months when DS suddenly started sleeping better. I had just given up on trying to get him to sleep in his cot and was sleeping with him on a mattress on the floor. After a few nights he was happy to sleep there alone. I realised - I had been so busy trying to do what I thought I should; trying to avoid 'causing problems' by not having him sleep in the cot, that I wasn't listening to him at all. All this time he was trying to tell me: Mummy! This isn't working for me!

When you hit a rough patch I reckon the best thing to do is whatever helps you to ride it out with the minimum of stress. If co-sleeping with your DH elsewhere is what works best right now, then, seriously, I suggest you do that. When she settles down again and you're all calmer and rested, then you can try to change things again.

They seem to survive just fine on broken sleep . Can't say the same for mum & dad of course.