I understand that you are trying to be friends but you just stated that trying new things sexually is something that you want in your newly single life. If your Ex is friends with you he will understand that it's something that you want and the fact that he's not dating you anymore kind of limits what he is entitled to disapprove of in your life. If you were dating and he was uncomfortable with it then obviously you would give it some though. But you aren't and he just has to learn to respect your wishes. Maybe just do it and don't tell him or look outside your mutual friend circle. Point is you are your own person and you don't have to answer to him. Also maybe some time apart after you just broke up to gain some perspective on your newly single identity's. If you just broke up he still may be in "boyfriend" mode where he worries about you out of love and habit. If you give it a few months and come back to each other as friends after you've found out more about yourselves he may feel less invested in worrying about what you do lol.