I would contact Pro-Ject and ask them to make a recommendation. That a clamping device wasn’t included with the turntable suggests it sounds best without one. You will need a threaded spindle to use a clamp. It can flatten a warped record somewhat but don’t expect miracles.
I prefer a weight. My turntable sounds better with one and once the platter (it’s heavy) is spinning, I don’t have to turn it on and off to change a record versus a clamp.