Sorry to hear about your struggles with the 'rollercoaster' as you described. It's awesome that you can come here and share and hopefully find others in your shoes.
I have experience with major depressive disorder so for the most part my mood and concentration stay the same. But during the troughs of my depressive episodes I am also struck with bad anxiety which can make each day feel like a rollercoaster as well. I've found help though from a mixture of treatments including self help, counselling, medication and others. However it always comes down to the individual and how they uniquely respond unfortunately. But my psychiatrist always assures me that there are always options and I hope you discover this too.
In terms of not wanting to be 'just ok', I totally understand. I just had a similar conversation where I mentioned that I don't want to be stuck at 80 or 90% and I feel like this is the reality for most people with mental health issues. And there is no reason to settle, we can strive and eventually reach 100% and the ups, downs and frustration along the way becomes part of our journey. Hope that makes sense. :)