Slight differences in white balance, even after calibration, preclude the use of multiple monitors for myself as well. Even if they are the same monitor, same model our nervous system is very good at detecting these differences.

I have no settled on a new monitor either, I'm using a 24" that is slightly too small for split screen use, but doable. 27" would be nice but 32" would likely be the best here.

There are a few good ones in the works. LG announced a new "IPS black" technology, which offers better contrast than your MacBook screen (claimed 2000:1, we'll see). As well, LG is manufacturing a few monitors for Apple this year. Some of these will be miniLED like the XDR display, but cheaper as manufacturing costs have likely reduced significantly.

The only monitor I'd even consider right now is the LGGN950 or one of the 5k2k displays, though the latter are notoriously finicky I've heard and currently not usable on Mac without a dedicated GPU.