I'm considering one or both. At a full length of 3-4' of which 14-19" is head and torso, a lizard of 8" or less should be fine.

The optimal lizard long term would be able to survive living with the mangrove. At the moment I am highly considering getting an anole to throw in with my savannah. It should be too small to eat the anole, and the anole should help with the crickets for the time being provided it doesn't get stressed to death.

I'll have to consider if the gecko will be a better long term option for my mangrove monitor. Being smaller, it may be better able to survive and thrive in there with it. Although if it eats bugs I may need to do the stupid cricket thing again in the adult enclosure.