You say you want a serious relationship that is also 'naughty'. Look, almost all serious romantic relationships at this age involve a sexual element (this of course can wane over time).
Unless there is a reason why not, at your ages it is assumed that sex will be part of an adult relationship. If not, it will usually be mentioned (e.g. asexuality or a medical reason).
You don't have to go into all of that in detail prior to meeting someone and it's actually best that you don't.
You have no idea if you will want to proceed sexually in person without meeting, so best to set out what you're looking for, quick chat, meet for a drink, coffee, or lunch, whatever, then decide whether you would like to see them further. You'll either fancy each other or you won't.
I once made the mistake of getting into sexual chat with a guy, met him and didn't fancy him at all. He did like me and it was excruciating!! Luckily it was only for drinks and I had a train to catch rather than having to deflect plans to go home that night. Lesson learned. Pre meeting chemistry isn't real.
You don't want a fixer upper. You don't want an oversharer. You don't want a timewaster.
Once more for @AccountCreateUsername naughtyyyyy