I have a couple ideas and questions for you. To start, I want to emphasize that having sex with a stranger does not make you a "slut" and it is not a morally bad thing to do. So know that even if that is said it doesn't hold any value. You are not lesser because you like sex and don't mind having it with strangers. I'm curious to know who you are worried about calling you a "slut" and if you wanted to talk more about that.
Further, I do want to challenge the idea that having casual sex makes it easier or more inherently pleasurable. I say this because I don't want your expectations to not be met. What about casual sex to you makes you feel like you will enjoy it more? Does it have to do with emotional connections? Casual sex can be just as complicated as a relationship and takes a lot of active communication and boundary setting, which can be awesome. If that's what you're looking for then great! But it does still require work because even though it's not a romantic relationship it is still a form of a relationship and that requires communication. Especially if the person you are having sex with is also a friend because feelings are complicated and it may change the dynamic of your friendship.
Stranger sex carries some big safety risks. Can we talk about them?
I think these pieces might help you think about how to navigate relationships with sexual partners.
Be a Blabbermouth! The Whats, Whys and Hows of Talking About Sex With a Partner
Would Friends With Benefits Work for Me
I'm curious to know more about what makes your previous relationship seem "stale" and what makes sex "dull" for you. The reason I ask is sometimes there are new ways to try to achieve what you want which is ultimately sex you enjoy (from what you've said). Have you tried different kinds of sex acts that might engage you differently and maybe provide new sensations of pleasure? Unfortunately, media and society has created a very narrow-minded view of what sex and pleasure can look like often limiting it to penetrative sex when the reality is that is just a tiny piece of the incredibly large puzzle of pleasure. I'm going to include a couple articles that might be helpful in your desire to find pleasure.
With Pleasure: A View of Whole Sexual Anatomy for Every Body
Yield for Pleasure
Now, I've jumped from communication to pleasure and desire for a reason. If you are trying to start a friends with benefits relationship it's really important to go in knowing what you really want. If after reading some of these articles and posts you've found that you really want to try different forms of sex and change up what pleasure looks like for you than maybe relationships aren't completely the problem. If you're hoping for a hook up with very little emotional attachment, that can be difficult if the person you are hooking up with wants that emotional attachment. There's a lot of different things you can reflect on but the overall point here is try to take a minute to interrogate what you really want right now because that will be extremely important in being able to articulate what you want with someone. I think you can do this if its what you want! I have confidence in you!
With all this in mind, what are you thinking about?