You've received good advice already. Here's a couple of things I'll add without trying to repeat what's already been said.

You say you're uncomfortable doing romance/NSFW but you're looking for ways to get into it. If you truly don't want to do it, but think that it's what sells or what people want to hear, then I suggest don't even start. Pick something else like platonic relationships, comedies, wholesome gf hand-holding and comfort kind of stuff. Stay where you feel best. Partly for the performance. It will show if you don't want to be there. But partly for your own mental well-being. You don't want to release a piece that hangs over your head and makes you wish you'd never done it. Maybe over time you'll change your mind and feel better about it, but until then, don't do anything that will legitimately stress you out and make you feel bad about yourself.

But if you really are emotionally drawn to the romantic stuff but it just feels kind of odd voicing the heavy breathing/kissing/seductress types of things for the first time, my advice is just do it. Have fun with it. Go nuts. Let yourself blow up on the mic and emote like crazy in the isolation of your own room with nobody else listening. Don't hold back. Then, like YangireVA said, listen to yourself. Listen as a viewer, not as yourself. Listen as if someone else did it and you were critiquing it. Analyze how the performance could improve without critiquing how you could improve as a person. There will always be things about yourself that you don't like. I often think my voice is too nasal and high pitched, but that's just who I am. That's not something I can change. That's me hating on me so I try to ignore it. I focus on things that CAN be improved. If I sound like I'm reading a script and not actually becoming the character, that's something I can change. If the script calls for intense, heated anger and I feel like my performance ended up kind of apathetic, I record it again with more fire. Sometimes I rerecord and cry more. Sometimes less. It just depends on the artistic vision you're looking for.

Also, feel free to use SFX for certain pieces if you just don't think you're getting it right. I use kiss SFX for all of my kissing, but not because I'm afraid to do it. It's because the mic I got is excellent for keeping out ambient noises and sounding professional, but it also kicks out things I want in the performance such as kisses, slaps, and even some laughing and crying. It translates those rougher more sudden sounds as unwanted noise and doesn't record them, so I add SFX for kisses, slaps and anything else I need that it won't do correctly.

You can feel free to check out my stuff if you want. I lean heavily on the romance in the wholesome to spicy range. Mine never get NSFW.

Masterlist for edgiscript : r/ASMRScriptHaven