Flip turns

Did a search and couldn't find anything; apologies if this is addressed elsewhere. I really struggle with my flipturns. What I took for granted in my youth is now quite a challenge. I find that I'm much more worn out after a swim if I've done flipturns, and I don't think I swim any faster or more efficiently when I do flipturns. It's difficult to pace myself consistently, so my approach to the wall is the first problem I encounter. I try to have about a foot or two between my outstretched arm and the wall before I begin the turn. Even if I manage to do this successfully, I find myself sinking quite a bit during the turn, so much so that I can't flip in the shallow end of the pool without scraping knees and elbows on the bottom! I'm a distance swimmer, so I'm not sure speeding up will do me much good in the long run. Suggestions for a better flipturn are appreciated.