Universal fit seat covers?

Hi I'm new here~Just got my 2004 Celica GTS.

It's been very hot here since last week, and the front seats are sometimes extremely hot. I have an accordion sunshade, but sometimes I just park my car for a couple of minutes and do not want to put it on, and even these 5 minutes can get the seat intolerable, so I have been looking for a seat cover, maybe made of mesh fabric which won't get too hot in sunshine as the leather.

My friends have been warning me not to buy any universal fit seat cover because I may slip with the cover when I hit the brake. But a custom fit seat cover is more expensive than I wish to pay. I wish to know if anyone here uses a custom fit seat cover? What's your experience with it?

Thank you!