So I'm not too experienced with this but can give some idea.
With a mini stallion you can just get down on the ground and let him go at it. Really you can do any position you want as long as its missionary or doggy style.
Full sized stallions most people will take from the side with the stud standing on all four legs as if being ground collected. That gives the most control over how deep they go and you can abort easily. Some will divert the stallion off a phantom or mare for similar reasons but you have a little less control there. You can lay on a bench or special phantom but you're at his mercy then.
It is totally possible to have a full sized stallion mount you standing up or leaning on a fence though. A stallion shouldn't be letting his weight rest on the mare when breeding her. Many do but they should be balancing most of their weight on their hind feet. You can see this happen when stallions are ground collected and stand up in the middle of it. I've seen plenty of videos with a man holding up a stallion but certainly something you have to practice at and a lot of trust in your stallion.
Hope that helps!