What should I look for in a diamond blade?
IMHO the main one that matters is "dry .vs. wet or wet/dry" - since you are using it in a normal saw which is not set up for coolant, you'll need a dry or wet/dry type blade. While I have known people dumb enough to try to rig up a water drip on a saw not designed for it, I definitely consider it a dumb move, as water gets into all sorts of things that are not designed to keep it out.

After that it's just shopping (i.e. pick a brand you trust, or the cheapest one you can find, depending on your personal preferences.) Shopping falls outside the scope of this site.

You might want to consider renting a wet saw, since using a dry blade in a saw is arguably somewhat abusive to the saw from dust being pulled in by the motor cooling fan. You will need to wear a dust mask, a well. A wet-type saw is going to greatly reduce the airborne dust, but they are generally too expensive to purchase for a non-pro - however, they can usually be rented.