Museum miniatures might fit well with xyston, minimally smaller. I like the unpainted bald archer on their website.
My initial suggestions were wrong. First, there is some advantage to using ranges that are all the same size, and Xyston are almost 20mm! (Don't hate, I spent hours getting 4 Xyston cataphracts on bases).
If you really want a challenge, go to the old Minifigs. Use the Assyrian spearman as your Egyptian spearman, then there are also Egyptian marines with axe. See how you are with replacing spears, and getting older figures to come alive.
But, here is much better advice. Go to Splintered Light Miniatures fantasy 15mm/17mm Egyptian. Skip the sons of Horus, or don't use many of them. I like sons of Anubis much better. Sprinkle some of those in with your Essex 15mm figures for real Egyptian flavor. Maybe a daughter of Bhat as well. Might throw in a few Assyrian deserters, use Old Glory 15mm fantasy men of Ashur. An unsung alternative to all Assyrian figure ranges).
I have both Essex and Xyston figures for this army. The Essex are good if you add a bunch of command figures, and I think there are a couple of poses in the Egyptian spear pack.