Solidarity Op, I have been through similar (3 early losses and a TFMR at 16 weeks). I don't have my happy ending yet but thought I'd share a few things I've learned along the way.
Background: I'm 38 now (my pregnancies were at 36/37 - two as a result of IVF). I have low ovarian reserve and my husband has relatively poor sperm quality (low morphology and quite high DNA fragmentation).
I've been told my history is due to poor egg quality because of my age, and the fertility clinic have encouraged us to use donor eggs.
However, I do think "poor quality eggs" is a "catch-all" / slightly lazy diagnosis when they're not really sure what is going on so we've been exploring other avenues first.
I had blood tests done for recurrent miscarriages which showed my immune system may have been responsible for "attacking" the baby in my early losses.
My husband has also been taking proxeed daily and recently had an operation to repair a varicocele to improve sperm quality.
Our next step was to do IVF but do PGT-A testing so that we could determine whether our embryos were chromosomally normal before transferring them back.
However, I found out a few days ago that I'm pregnant (naturally) again. Clearly very early days and I have no idea what will happen - I'm taking progesterone, low dose steroids and aspirin under the care of the fertility clinic to reduce the risk of early miscarriage.
For you, a first step might be to get recurrent miscarriage blood tests done. You would be eligible for these on the nhs given your history. You could get them done privately - they cost c£1,500 but I got mine covered by my work health insurance.
Really hope you manage to get some answers and some better luck. It's pure torture living through this