I think we all overthink this topic and end up communicating a lack of confidence which in turn impacts sex life more than how big our breasts are.
In general, I believe most women want confident partners. Easier said than done, especially in our world full of constant advertisements and messaging for testosterone boosters and chiseled men and busty women.
I actually think many couples miss out on a whole world of pleasure and intimacy when they lock themselves into a rigid idea of masculine expectations and approved forms of pleasure.
If it feels good to have your breasts/nipples touched or played with why would you want to avoid that. Be honest with your partner and you might be surprised.
My partner actually likes to play with them. If you have sensitive nipples let them out to feel good. If you have an attentive partner and you are honest about your feelings, trust me you may likely find you have new buttons to push. And the feeling of your own nipples rubbing her nipples can be amazing.
But even if you don't have sensitive nipples you can still enjoy sex with your breasts hanging. Having breasts does not have to make you any less of a man, unless you want it to. Instead, like my partner says I'm a man with benefits. Instead of getting stuck on our identity as how masculine or feminine we are, our identity can instead be based on our love for our partner, on our good qualities, on our passions, on our faith...
Yes it may be hard to walk around in a world with breasts but when we are in our private time with our partner this should be a place of safety, acceptance, and intimacy. And if it is not then there may be some work needed on the relationship about communication and expectations.
As far as positions go, have you ever seen the kama sutra? Trust me there are hundreds of positions and ways of pleasing each other to have to worry about whether your partner sees your breasts.
For me, it's also practical, if it is vigorous lovemaking my breasts can bounce too much but having them held and played with makes a world if difference.
Besides, performing reciprocal love acts can be very pleasing, enlightening, intimate, and fun. Take turns pleasing each other. Consider asking your partner to show you what they want you to do to their body. This can open all kids of doors to pleasure and letting your guard down.
Keep in mind that your partner might not feel comfortable bringing up their own insecurities about their body with you. This is a two way street. They may be just as afraid to bring up what they like or dislike to you.
Good sex counseling, couples counseling, marriage counseling, or especially pre-marriage counseling will encourage you to communicate your fears, expectations, and desires about sex and other forms of intimacy.
I found that for me joking or being playful with my partner has disarmed some of the tension about this topic. Be curious and lighthearted. Ask what's the 3 best things they like doing as part of sex. Ask them what are things that they are less comfortable with. And be willing to be vulnerable and share yourself. Be genuinely curious in wanting to go deeper and find out what makes her tick.
Fear is always a bad motivator. It stifles our passions and robs us of joy and pleasure. I find focusing on what I want or like is a better path than avoiding a topic or a person. It can be very freeing to talk openly about this with your partner.
Yes there is a chance that your partner will not respond well or not be supportive. Don't get mad but just take it as information and move on. Bottling up insecurities will not end well. It comes out in your health and other parts of relationship. Have courage to lead and communicate about this.