Sorry it's not got any better, I kind of hoped you'd say its magically improved
Do you have much support to help you cope? Can you nap in the daytime?
I know what you mean about the stiffness, I sometimes wake up with a dead arm! We change position - switch sides etc, which helps. If you're a wriggler though I guess it's more tricky. For me it's just been trial and error really. It was a relief when I realised it's fine to move and shift position. I find baby settles very quickly when next to me, so I can wriggle about a bit until I'm comfy.
I can't remember your OP, do you have him in a crib next to the bed?
I read somewhere that babies are kind of naturally drawn to mum's chest, and that this position means you're pretty much face to face. Apparently this is great for them because your breath on their face stimulates their breathing so they have leas irregular breathing than if they we're on their own. Of course babies are ok on their own too, I don't mean to give you anything to worry about, but I just mean that safe co-sleeping is pretty safe, even with big boobs
Safe being no alcohol/ drugs, safer if you're ebf, no bedding that could get them too hot or wedged in somewhere, etc - there's stuff online about guidelines.
Also - what's the big picture like? By which I mean how's baby's feeding, health, do you wind down before sleep time, could he be getting over stimulated or over tired before you start getting him off, wind/ reflux, etc?
Good luck tonight.