I've never shot one, but I used to own a Taurus PT99, which is a copy of the Beretta 92 (basically the same guns), and I'd say the P38's grip isn't that much smaller than the PT99 grip. Yes, it is a bit slimmer because it's a single stack, but not much smaller. The PT99 had a better trigger, a much better balance, and a more comfortable grip for me. And to top it all off, it ejects to the right, as opposed to the P38's left hand ejection.
You should try to shoot one, or at least hold one, before you buy. I was about to buy one two months ago, but I waited until I went to a gun show to actually hold one in my hands. I'm glad I did, because that broke the deal, I didn't buy it.