There are a number of books out there that are for Oboe that have been adapted for Saxophone. Ferling’s, and Rossari’s books would be two examples. Another great book to check out is “Vade-Mecum of The Oboist” by Albert J. Andraud. The 200 page, over sized book contains 230 selected studies (some from Ferling) and Orchestral excerpts to hone your skills. Though it is for the Oboe, it works great on saxophone. This book does not pull any punches. It starts hard and keeps it there.
For those looking for some technique etudes, this book will not disappoint. 9/10 (1 point deducted for the oversize of the book which I don’t particularly care for).