I have been fortunate to train my baby to "like" tummy-time since birth. After feeding, I'd put her on her tummy and even when sleeping. I know it's a risk factor for SIDS but I was not worried because she can turn her head side-to-side since day 1 and we we're careful not to put pillows or blankets that could suffocate her. Up to this day, she even prefers being on her tummy and would protest if put on her back.
At 3 mos, she can turn-over both ways. At 3.5 mos, she belly-crawls and at 6 mos, she can criss-cross crawl. Come 6.5 mos, she can stand without anything to pull-up on. I really believed that "training" her early on helped with her mobility.
I am going to let my next baby sleep on the tummy like you did. I don't think it is a big risk factor for SIDS if you have a strong baby and not a lot of congestion, blankets or pillows.