Agree with Monty that the Clicker is a good one (3/8" tube). The body (tube) is a bit on the longish side. It can be problematic if you don't have a good driling system. Otherwise a well-built and straight forward pen.
Other options: The Guardian Jr (from PSI) is an interesting pen. Looks fairly big and it is. But I've sold several, a couple to folk with arthritus. They seem to like it and appreciate the soft grip. If you are into REALLY BIG pens, check out the Guardian (not the Jr), also an 8mm, it's HUGE.
The Power pen (again from PSI) is an 8mm click pen. Kind of basic, but servicable. Personally, I find it "bland" and slightly on the cheap side.
And, lastly, take a look at the Apex (from PSI - no, I'm not on their payroll). It's an 8mm new arrival from them. It is "feminine" in appearance (to me). It has some heft, though, and is an interesting turn. I thought it might be top-heavy, but LOML got the first one I did for Christmas and she swooned over it and says it's great.