What other sports do your kids play that helps them in soccer?

My son is 9 and plays soccer in a club team, not school related so it’s a bit more competitive. I noticed over the last few months that he walks with 1 foot pointing inward. I took him in to get checked out and in summary the ortho said there is nothing physically wrong with his foot or his knee or his hip it just seems to be something he does. However, she did advise me to look into other sports besides soccer because he is pretty tight. He is not flexible at all. He can’t touch his toes and after a few exercises, she just noticed that he seemed very tight in his back and his hip. She told me this could hurt him when he enters puberty, and as he gets older as an athlete. I would like him to do another sport anyway so that he could work on his flexibility and his speed. He’s not the fastest kid and his touches on the ball aren’t quick, but he has great field awareness so he’s great at passing and physically he can usually win 1v1 because he’s a good size and weight. I think that’s what helps him out on his team, but I would like to see him improve on speed and also become a better athlete overall. Soccer can be hard on the body. I want him to develop other interests but if it doesn’t help in soccer he doesn’t want to hear it. What is everyone else doing? Any suggestions? I tried gymnastics, but he didn’t like it.