Im on the heavier side..and so sitting crossed legged was a challenge...especially when I wanted to go to the temple...or have a festive meal - the plate would be on the floor..cant be picked up..has to be eaten by hand..no spoon.. -_-
What worked the best for me...was sitting cross legged..as much as I could..on the floor everyday for a meal...and butterfly stretches. Also, if its easier for you... try to put your hands under your bum when doing this position, it helps... because while the legs are adjusting..the arms provide support... :)
Good luck! hopefully it helps :)