Hi Will,
I would suggest using a UV-excitable GFP. Excitation max. is at 399 nm, but it is still efficiently excited at 405. Emission is identical to GFP.
Co-imaging with ordinary GFP can be achieved by switching the excitation source. The only downside is potential cross-talk, although excitation of UV-excitable GFPs at 488 is minimal.
The best variant that is published is mT-sapphire. We have recently made an upgrade of that; LSS-SGFP2 (large Stokes-shift SGFP2). It is 2-fold brighter (unpublished) and available from addgene.org: https://www.addgene.org/browse/article/22612/
Don’t hesitate to contact me for further details…
Best,
Joachim.