My own personal opinion is that this might have less to do with you wanting your mom to know vs you just wanting to tell someone in general. Just like was brought up in a previous post in this topic, people have a need to talk. Perhaps you feel more comfortable telling her because you think she will be more accepting than a friend or another family member would. I mean in most cases who is gonna love you more than mom, right?
If you want/need to tell her then do so. Yeah, I agree she probably doesn't need to know about your sexual activities, but while the topic is sexual in nature I think the overlying issue of wanting to be accepted in whole by your mother might be worth it.
As for how to tell her, I know how you'll feel compelled to mention it not having anything to do with kids, but your best bet is to let her bring that issue up. Don't put the thought in her head. Be prepared for everything and anything. She obviously suspects it if she's caught you twice, but while she might know she probably hasn't prepared herself to deal with you wanting to wear 24/7. Good luck whichever way you choose.