Hey choccy sorry to hear about your recent mc.
There are quite a few of us who've been up to Coventry for nk cell testing (me included), and had similar experiences and conversations.
I am "super-fertile" so accept everything, only to reject it again later, and have had 5 MCs before 6 weeks. I took an enforced break from TTC after my last mc in Feb as I was physically and emotionally exhausted, and saw Prof B last month.
He described a similar protocol, with progesterone from day 19 (I have a short cycle) and heparin and predistone once pg confirmed in the right place. I had the biopsy and am hoping to get the results early next week.
In the meantime, the effects of the "scratch" from the biopsy are meant to help with the reset too.
So, here I am, with a positive pg test yesterday, and possibly my final attempt. It is scary, but I feel like I've exhausted all the tests I'm comfortable with.
The biopsy is £360, you're right. I whacked it on a credit card 
Personally, (and it is entirely personal, so feel free to ignore me) I would start using protection in case you haven't caught yet. Give your body and mind a rest for a couple of months and explore nk cell testing, and then you can make an informed choice about where to go from here.
Women have been successful, even after as many MCs as us, so holding onto hope is a good thing.