Sounds like you have a background in Cardistry, and that will help since you're familiar with proper technique for cuts and shuffles. Do you know the clipshift? I believe there's a bit at the beginning of that move that can be used to get a break above the bottom card.
As far as books go, Jason England's what to read video sums up my recommendations rather well and throws in a few more. I own Royal Road to Card Magic, Expert Card Technique, Card Control by Arthur Buckley, and Erdnase, along with a few books on general magic. All of those are excellent books for someone who's serious about magic. I have a strong background in the older literature of magic and I can honestly say that while the tricks aren't always presented in a modern fashion, and the handlings could be updated, but the underlying effect is always something worth trying.
I'll try to get a video or something sent to you for the method of catching a break above the bottom card. Basically you take the deck in biddle grip and use your fingers to pull the bottom card out and eventually it pops free of the thumb and falls into a position where you can get a thumb break. That's a terrible explanation, but you might be able to work it out from there.
I noticed you're located in Germany, so I'll add this to my recommendations. Books are great, but sometimes the older ones that I read take a while to comprehend, even for me with English as my only language. If English is your second language videos may be easier, but if you're willing to take the time to either find books in your first language (I assume that would be German), or to read and try to comprehend books in English I can promise that you will not be disappointed. I always tell people to go buy books because they are the best source of information, but when you have trouble understanding the language the books are written in, videos are a much less frustrating solution.