I'd stick with powered monitors. Even the really high-end stuff is going mostly powered now (e.g. DynAudio, Genelec, Focal, et al). And that saves you the math of trying to optimize the amp with speaker's expected impedance & min/max power handling.
Not sure what your budget is, but Focal just came out with a series of really inexpensive reference monitors (inexpensive for them). They start at $299 each (so like $600 a pair). When you consider that their pro reference speakers are $1900 each, that's quite a deal. You can check them out here:
https://www.sweetwater.com/store/det...studio-monitor
I really (really!) like DynAudio monitors, they have spatial imaging that is so precise & a super flat response...but their cheapest option is the Lyd 5, which comes in at $600 each. So not really a budget option. You can check those out here:
https://www.sweetwater.com/store/det...-monitor-black
Of course the other models mentioned are being used in small project studios all over. Of those I probably lean towards the Yamahas...but that could be because of all those years of having NS10s as my 2nd set of monitors.
In the end you need to go with what you like that fits in your budget. Once you learn a set of speakers you can make good mixes on them. You'll just need some time to get comfortable with whatever you end up choosing.
Also keep i mind that the smaller speakers are not giving you any of the real low end. The Yamahas stop around 54Hz, the DynAudios cut off around 50Hz, and the Focal cut off around 45Hz.
All of those are low enough for guitar (low e on a guitar is around 83Hz) the low e on a bass guitar is around 42Hz. So even if you drop your low E to a C for alternate tunings, any of those monitors will be fine. It's just as you get to full bands or lower instruments that you will be "mixing blind" on the low notes.
Hope that arms you with some good info for your search.