Just make sure whatever phone you buy will work with your current plan and provider.
If you want a low-cost provider, I’ve been using Mint Mobile for several months and haven’t noticed any difference from my previous provider. By committing to a year, I’m paying $15/mo for unlimited talk/text and 4 gb of data (you can pay more for more data if you need it).
Mint sucks for international roaming—BTDT.