Please don't feel inexperienced or embarrassed, the things we're talking about aren't very well-known at all! There are a bunch of stereotypical ways to masturbate that everyone grows up seeing and hearing about, which don't work for many of us out there, and I think it's worth celebrating that you've had a strategy for years that always brings you to orgasm.
I understand your fear about potentially not being able to reach orgasm when you have partnered sex. However, I think you may find that partnered sex has different things to offer than solo sex. It may be emotionally more charged, or physically more charged, because there's another person there to command your attention, and because you're not just focused on your own body and your own thoughts. Orgasm doesn't even have to be a goal, because it's fun simply having sex and being in the moment with someone else. At the same time, orgasm doesn't have to be impossible: you said that fingers and clit-rubbing does give you some pleasure, it just doesn't cause an orgasm. When you're having sex with someone else, you can start off with those, and do other stuff, and then when you feel like you're getting close, you could shift to your regular heel strategy! I promise you that it isn't as weird or uncommon a strategy as you think it is. In fact, the person you're with may just be super into it. Also, like Sian said, it may help to figure out exactly what it is about the heel strategy that works for you, and try to replicate it using other things. The heel of the palm may work similarly, especially if it's a sex partner's hand, because they can increase the pressure more freely than you'd be able to with your own palm.
If it's giving you any pleasure, it's good technique! And it is by no means uncommon or embarrassing to have a difficult time with just fingers, lots of people can't get off with just fingers. Pleasure is the goal here, not conforming to stereotypes about how people get off. Since you've already found a strategy that works perfectly, you should totally just build on that, and have fun doing it. Does that make sense?