@editor We have insulated with hempcrete and iso-hemp blocks. More expensive than foil backed foam but as a breatheable/moisture permeable material does not need all the membranes and is better suited to our (no damp proof course 1880s) cottage.
Draught proofing of windows done this weekend. Check.
We've tried using an endless amount of products (caulks, silicone, fillers, etc.) to draught proof our windows, and they never seem to last more than a few months before they start to crack. So we've turned to our go to all-in-one product, Maxam's DURA+, to draught proof 29 windows across the property. It's been a winner of a product so far, from sealing our shower to sticking a broken slate step together, so we're optimist it's going to work sealing our windows, keeping draughts out this winter (and the heat in): https://myhomefarm.co.uk/draught-proofing-windows
DURA+ on Amazon: https://amzn.to/3FsDYiQ