There have been studies debunking claims of bike-induced ED, buuuuut, if you are really worried, you can get a ventilated or slotted saddle and occasionally stand up on your bike at traffic stops and such. There are specialized saddles and a variety of bikes with different riding positions.

I love downhill mountain biking, singletrack, and city riding, and never had issues with getting it up either. When the shitty OEM saddle made my balls fall asleep, I swapped to a better saddle made by SQ Labs and changed the seat angle slightly.