I’m happy to share what I know! I’ve been making cotton strings for a while and they’ve been turning out really nice for me.
These are type 6 cotton with about 12% reduction, pretty standard recipe. I use a swivel for the final twist to keep the axle loop as small as possible which I think helps with response a bit.
Apart from that it’s all about twisting, stretching and adjusting the string as you’re breaking it in. This is by far the most important part. Mine end up looking like this:
This is just what works for me but cotton is super adjustable so you should be able to get most cotton strings working how you want them to with a bit of tinkering.