Hey, Break Free: where are you from? Your English is fine... better than a lot of the "English-is-my-first-language" types who post on TB!
I recommend buying 6-string bassist Todd Johnson's "Technique Builders" DVD - best of breed, IMHO.
You don't need to read music to use it & Todd guides you through various technique drills and exercises, kind of like having a buddy sitting in the room with you showing you stuff.
You don't have to do the "floating thumb" thing he shows you, either - the rest of the DVD is directly applicable to anyone who wants to improve bass technique, floating thumb or not.
He has a forum on TB under "Ask a Pro" - check him out. If you live overseas from the U.S./Canada, this is a Region 1 NTSC DVD I think - you may want to check with Todd about that (he's a nice, patient guy).
I've had this DVD for a while now, swear by it, and I constantly refer back to it to fine-tune my technique. It is definitely "technique-specific", so you'll have to get the theory & reading/sheet music stuff somewhere else. (Like Ron Velosky's excellent "Sightreading for the Bass" book.)
JMHO
p.s. - just fyi, I personally did make the change to "floating thumb" due to beginning-carpal-tunnel issues that were starting to raise their ugly little pointy heads in both hands, and wouldn't go back now even if I could... esp. since it solved a number of muting issues, too.
YMMV