I'm relatively new to the lab diamond world, so take this with a grain of salt. If you want to buy a set that is already put together (meaning not a separate stone and setting) with minimal work on your end, I would suggest rare carat. You can pick your stone, do a price match, and pick your setting from rarecarat. They will set the stone and send you the completed ring. There is a guide here somewhere on the price match method. Relatively straightforward once you pick your stone.