You can change the seat heater switch so it just stays on the same setting till you turn it off. Check the manual. The vented seats are more effective in the summer with the air-con turned down, I can attest to that with my holiday to Italy during the summer and outside it was 35deg.
ignition on press and hold both heated seat buttons until a beep is heard ,your seats will now stay on which ever setting you choose,without the heat setting reducing from 3 to 2 to 1