I don't like ecoearth but plenty of people do. I like reptichip, plain old paper towels, or aspen. You don't have to quarantine from each other but you do have to from any other reptiles in the house. Paper towels is the best in my opinion until you know if they have mites or not easier to spot them on white.

Boas do get big eventually. Not Retic sized usually but still pretty big.