Yoga isn't the only place to deep breathe or stay with our breath! The way a teacher encourages you to check in with how you are breathing? Yeah, you can do that for yourself or your partner(s) during sex!
Notice your breath during sex. Are you breathing deep? Are you holding your breath? Are you letting yourself exhale and be loud or stifling your breathing and any authentic noises?
When you're in tune with your breath during sex, then you can start to play with it! See what it's like to breathe along with your partner(s). Do you feel more connected? Synced up? Or see what it's like to consciously hold your breath. When we do this, our muscles tighten, kind of like before an orgasm; then you can notice what it's like to take that big exhale and settle back into yourself. Are you more present? Able to notice more body sensations?
Another way to bring in breath play: Have yourself or your partner hold their breath as a safer alternative to breath restriction (i.e., hands over someone's mouth or on their throat, which can be done safely but does have some obvious health risks). Because this is sex and not yoga, being told what to do or telling someone what to do can be hot. Consider taking turns telling a partner or having them tell you to hold your breath, release, or lean into it. Notice how it feels to be more or less in control.
Those are just a few mindfulness tools that can work wonders in the bedroom for some people. Take what works for you here, and leave the rest! The whole point is not to “be better” but to connect more deeply with yourself and your partner(s). There is no right way to feel or experience pleasure. You're not “doing it wrong,” and if this isn't a place you can go during sex, there's also nothing wrong with that. Just notice what works or doesn't, and be curious about why that is.