Only thing I would suggest other than play more is to use low sensitivity if you're not already doing so. I use 400cpi with 1.0x ingame sense and 1920x1080 resolution. I don't think you necessarily have to go that low, but having a low sensitivity makes it easier to keep your clicks from effecting your aim. I would also recommend using the same sensitivity playing osu as you do using a computer normally to build muscle memory.
I don't think mouse only is as hard as some people would have you believe and its lots of fun, literally just clicking on circles! Its strength is also its greatest weakness, you don't have to worry about coordinating between two hands doing different things so jumps can actually be easier, but its also harder to separate rhythm and aim making streams and complex rhythms harder. I also think it develops skills that translate better to other games and using computers in general, but the difference is probably pretty negligible. Just my opinion so please take it with a grain of salt.