Many racing planes use a flat bottom wing or partially flat. But a lot thinner.All trainers have a very thick wing and usually flat. Flat is good for lift and many designs do not increase drag it is largely the thick wing with an airfoil designed for high lift at slow speeds, not just because they are flat per say. I have a scale model of a T6 with a flat bottom wing that is very fast.

For the OP, I would suggest one of the 90 or even 1.20 sized sprort planes. Perhaps the large super sportster which was designed by . You could probably handle some of the slower pattern planes but generally the sport planes will fly and land a bit slower.