I had a similar problem as a natural. Not that I had a problem retaining length, per se. I grew my hair to mid-back length, but I did it by doing C& G - two months in extension braids, two months out of extensions. When it was out of extensions, I wore it in twists for two weeks at a time. Very low manipulation. However, those detangling sessions after washing every two weeks were horrendous, and I sometimes had a whole lot of single-stranded knots. What's more, since I was in extensions or twists most of the time, I didn't get to enjoy my length, or even to really know that it was there, until... I relaxed and had bra-strap length hair even after the stylist took off three inches.
Since I was iffy about the relaxing, I tried to go back to natural last year, but couldn't hang with the tangles and shrinkage, and didn't have the time or patience to do the twists and extensions anymore. My hair was just frustrating to me and I felt like I was breaking it off every time i tried to fight through it. I also wanted to enjoy my length. SO I decided to relax again. Not because it can't grow long while I'm natural, but because I am not at this moment prepared to do what *my* natural hair requires to grow long. But I do believe my hair per se is stronger and (if I didn't have to comb it) retains better when I'm natural. SO if I could find a way to stretch my natural hair out without compromising on strength, I would be one happy camper.