If planetary is your focus at the moment and if you can tolerate the relatively short eye relief, then I'd suggest something minimalist, a decent plossl or ortho would do a nice job.
The focal length isn't so simple... with your current spread, something around 200x would sit nicely in there, for the half decent nights when the 6mm is too much, but you think you might squeeze more out than the 9. Ideally a 7.5 but the market seems to be fresh out of those
which leaves either a 7 or 8, depending on what your local seeing is more likely to allow you to use the most. However, I can't help thinking it'd be getting a bit too granular, and you might be better saving your money
If your 9 is the factory bundled then these tend not to be the greatest on early and it might be worth looking around for an 8 with decent glass - TV Plossl, Hutech/UHD ortho, BCO, and don't forget to keep an eye open in icetrade
