Auto Parts have steering wheel wraps that you lace on, it would be too big, but you can cut to your needed size.
As far as not getting hot out in the sun, I don't have any answer for that. But if you park it inside the wheel will be more comfortable & coller, & when yoiu are mowing your hands will be moving on the wheel, so that'll help.
PS: I have also saw some velour wheel wraps that use elastic.