It doesn't say if people need to get the third shot from the same vaccine as the second shot. My spouse and I both got Moderna... Actually, I think my mother, one brother, both sister-in-laws all got Moderna.

Do we need to get a Moderna booster, or could we/should we get a Pfizer booster?

It doesn't, but I strongly suspect that the recommendation will be that you get another dose of the same vaccine.

The vaccine manufacturers have been running trials to see the effects of a third dose, and as far as I know, they were only looking at their own vaccine. Pfizer started such a trial back in February.

I think there may be some mix and match trials being done, possibly outside of the US, but I don't think they're anywhere near having the results yet.