My cell phone crapped out and I want to just buy one on ebay. I have several questions about this process. Can you help me?

So, I have T-mobile, and my phone has a sim card, which I still have. Do I need to buy a phone that specifically says “unlocked” or will any new phone do? In order to use my sim card, do I need to but the exact same phone I had before, or can I buy any motorola phone, or just any phone that uses a sim card at all?

Thanks!