If you have large hands, a TWSBI 580 might be a better pen (although it's not cheap). I have a 580-AL and it's a fairly heavy pen -- although it does hold a lot of ink. The only quibble I have with it (other than the weight -- it's now my benchmark pen, where anything heavier is *too* heavy for me) is that the piston does not go all the way to the back of the feed. I think this is a design flaw, because if you get an air bubble in the chamber it's hard to get the rest of the ink down to the feed sometimes.
Have a look at the Goulet Pens website -- they have technical specs for all the pens they sell, including the length (both posted and unposted) and weight (capped and not) and the girth of the pen. Do some comparisons and see which pen(s) might fit your needs, and that may help narrow down your choices.
Ruth Morrisson aka inkstainedruth
ETA: I suspect that the problem you had with the Preppy and the Parker converter is that they weren't a good match. Parker cartridges and converters are proprietary (and while I have read that they fit in Aurora pens -- and POSSIBLY in a Lamy Safari) they really are designed for Parker pens. Other brands take International Standard cartridges and converters, and you can use any International Standard ones. I don't know about what Preppies take (I have a few, but use them as eyedroppers), but I believe that in general Pilot may also be proprietary cartridges and converters.
Edited by inkstainedruth, 27 April 2018 - 14:38.