Here is a link of several choices:
https://www.amazon.com/bike-pedals/b?ie=UTF8&node=3404891
.
For me there are several factors I consider: I don't race, I commute by bicycle so want flexibility and simplicity (don't want to carry 2 sets of shoes!), my bikes (Q559 and QX100) both are configured with the pedals a little lower than the bike seat so gravity helps just a little bit to hold my feet on my pedals. I don't use a trainer, but some of my ramblings here may be of use.
I say gravity helps hold my feet on the pedals a little bit because if I hit a bump my feet may not stay on the pedals, but I just relax and slowly spin my feet "as if they are still on the pedals" and they usually land back on the pedals.
Unsafe maneuver at best, because if my feet don't land on the pedals I coast to slow down a little and try again! I don't know if this would be a problem on a trainer.
My current pedals are Shimano A530 which are flat on one side and SPD on the other side. I have tried clipless SPD shoes and loved the control and safety, but have not found shoes that don't hurt my feet since my feet are wider than duck feet, but I'm still looking for bike flippers!
There are many other options, on the above link and elsewhere, with both sides being flat where it would be more likely for your feet to land on a flat side of a pedal. Hope this helps.