Gosh,, I'm a tit. Usually I do read at least the OP's comments, but I got a bit carried away and didn't this time, sorry @Sleeplessem!
I see your position is intensely difficult - do you not have any relationship with your mother either, because that's what it sounds like (abusive home was her, was it?).
It does look at least like you're in the UK which is something - better than being in a different country and going through this!
I think there are other organisations you can contact than just Women's Aid, and maybe other refuges than those run by them.
But I can see that you will have to wait at least until you are back to work - is your baby going into childcare with the older child? Better than going to the MIL, by the sound of it! and then while at work you might be able to search for other options.
It's good that you have a plan, and that you will see solicitors - I know it's not a given but the courts don't usually discriminate against you because you had PND or anxiety, despite abusive bastard Hs often telling you that you'll lose the kids because of your mental health. They lie.
I hope that you can hold out and find a way out - if you haven't already looked up "grey rock", I suggest you do - it's a way to manage your own feelings when your H is being a cunt to you. You imagine that you are a grey rock and that you absorb nothing, nothing can hurt you, nothing can damage you and you reflect nothing back either. He can rage and storm at you but it will have no effect on you. It will just slide off you, leaving you undisturbed. It takes practice but it can be very effective, and has the added bonus of baffling them when they realise that their efforts to subjugate you aren't working!
Best of luck - vent away. 