Welcome to Thunder’s jelqjello.
What is your current level of experience with PE? I’m asking because clamping is an advanced technique.
I do not recommend forms of jelqing while clamped, this is a recipe for injury as there is a significant amount of pressure from just the clamping alone, add in a jelq and something is likely to burst. So yes, keep clamping to itself and jelqing with jelqing.
Jelqing in different forms, such as the slow squash jelq are excellent manual exercises. Jelqing will support both girth and length gains, just be consistent and use constant heat if you can.
If you have not already, the Newbie Routine is an excellent place to start.
Welcome to Thunder’s and stay safe!