I agree with the yoga recommendation. Just stretching your hamstrings is all very nice, but it'll be a lot more useful in conjunction with opening out your hips, and generally stretching and strengthening your body. Less chance of injuring yourself if everything is stretchy rather than just one part.
I really enjoy doing Astanga yoga because I love how doing the same sequence every time and just adding to it lets me get into my own practise rather than thinking about what to do next or following a teacher at their pace.