The Framers Forum

PFM website have a 25% discount on their books at the moment. Their delivery charges may be extortionate and it may be more use as a reference as to what's good and out there...I don't know. I can highly recommend the Greg Perkins Guide to design book. I subscribe to their magazine too.
https://pfmpubco.square.site/

Good plug Justintime

I can personally recommend Meg Glasgow's "RECHARGE YOUR BUSINESS"
I've lent to it to numerous framers, and they all said how it helped them.