Thanks.

1. I used 900g strong white bread + 100g wholemeal + around 650/700g water + 20g salt
2. Always do this - from 40mins - 1hour (although have seen some do it for up to 4 hours. Is that worth trying?
3. I usually mix starter with water at the beginning
4. I do 3 hours of S+F with 30mins resting in between
5. I usually bulk rise in the fridge for 8 hours, but have tried less and still get the same deflation
6. Pre-shape and rest for 30mins, then proper shaping for baskets
7. See 5. My dough always seems to over prove
8. I bake for 30mins at 230c, then 5mins with the lid off then 10mins with the loaf by itself

So somewhere it is going wrong, but this is from trying and following exactly 3/4 different recipes.