Hi Fio,
check some of my posts from the weekend, you will see my setup.
I have unglazed quarry tiles in my oven, and then on top of those I have an old pizza stone.
I do believe this works much better than just having the pizza stone there by its lonesome.
The tiles give a blanket of heat-loss protection and a source of heat to the pizza stone, as it cools, so I
am going to say that my stone has better heat retention like this.
Get over to your local hardware store, and buy some of these tiles. I paid 14 cents a piece for mine.
Anyway, it's an inexpensive way to test out your problem, and I will bet you a mug of frosty beer that
your stone will stay hotter longer.
From what I've seen on the net, professional pizza stones are much thicker than the one I bought ( el-cheapo )
( you'll also notice mine is cracked ) as it doesn't have the fibre lining the really expensive ones
do that you can buy online at different sites. Now, if high quality stones are thicker, and indeed they are, then I
believe I'm on the right track with what I'm doing here. It's far from perfect, but it's better for the time being.
Make sure to heat your oven a good hour before doing your first pizza.
By the way you are doing a lot of pies there, I haven't seen too much talk of anyone here doing them
one after another like that, so I'm assuming you were having a party or something, or .... you were
mighty hungry

Anyway hopefully more members will jump in with suggestions that can help you out.
edit: I've added a picture of my oven, so you don't have to go looking for it.
Mark