Hi omamjama,
Honestly there is nothing boring about farming mana at /slayer. I actually don't find it boring, especially at /slayer 3, while listening to music. The satisfaction of killing the mobs while listening to my favourite music never makes me bored- you can then use the mana for is upgrades, /rankup or even sell it for easy cash.
If you wanted to, maybe farm some mobs, for example I heard some people are trying to achieve 1 million mob kills. That's just crazy. The heads can then be used to /slayer or /Kilton... You get the jist of that.
Like what IceBarge said, though you aren't good at building, well now is the chance! Maybe look at building tutorials on YouTube and maybe make a warp, that can be useful, for example a mob farm, head shop, maybe a flower casino... There is so much time left and you can start by learning how to build- remember this will help you for future seasons (if you do play) or in general Minecraft. I also agree with what he/she said, try work on /rankup /is upgrades or even try to focus on little things like trying to get the magic title.
I hope this helps :D
Kind regards,
Eureka14, a fellow skyblock player