Maybe instead of different wheels, you could try
building you a strip. A roll of roofing felt, you
know, the black 'tar paper' makes a good runway.
If you leave it on the ground, it will kill the
grass from lack of sunlight, but after you fly,
you could roll it back up for the next time.

Or some old carpet or card board or plywood. any
thing would be better than the grass for the small
planes like you are using.

If you add bigger and heavier wheels, it will only
add weight and drag, and I dont think you want
this. The only other option that I can see is hand
launch. And it is a lot more fun to see the things
rotate and take to the air from the ground.

have fun, Roy