A testnet stake pool is currently being tested publicly. This was announced a little while ago here and you can use the stake pool here. It will be transitioned to mainnet shortly when a per user voting feature is completed on the pool. Then the code will be made free and open-source and anyone can host their own stake pool. The goal here is to transition it to community operation in full.

You can solo PoS mine, but that requires a wallet that is unlocked continuously and must be left on 24/7 for months or else you might miss an opportunity to be rewarded for your vote. So you can see the appeal of a pool as it does not require any of that. In terms of buying tickets, that has been possible since block 256 - however, you won't be rewarded for your vote until later, which starts at block 4096. So that will be happening relatively soon as well.