Looking at electronicstix, looks like the Zen mini is a tail-switch device. If that's what you mean by "bottom button", then you might check out the
Megalodon. It's available with multiple tubes, so it'll take different batts. Not sure how shipping is from across the pond.
Compatible battery sizes in 3.7 Volt format include: 18650; 18350; 17670; 14650, 16340; CR123A to name a few.
While if you want to experience some higher voltage vaping, the Don caters for 5 Volts (our own custom 5V battery); 6 Volts (2 x CR123A 3V); or 7.4 Volts (2 x 16340 3.7V)
Seems it out of stock at the moment, so checking with Moju might be indicated. I can't tell from their description which tube(s)/extension(s) come with it by default.