Well, mtn bike season is almost over (here in New England anyway) so why not wait 'til Chrismas and see what Santa brings? In the meantime be careful and try not to bust your n*ts by slipping off the pedals. Better yet, buy your pedals and shoes now and ask for a cool new bike for Chrismas.
Seriously, when you climb you obviously have weight on your pedals but make sure when descending, you not only get your weight back, but keep it on the pedals and not on the seat. This'll both help keep your feet on the pedals and lower your center of gravity. I'm not sure what Sketchers are but do they have heels? If not, try riding with shoes that do have heels. Best of luck.
Great advice above from Dylan also.

aj