My first recommendation would be to try the seat before you buy it - both by physically sitting in it to make sure your comfortable, and to see if it will even fit in the car. Some seats (even expensive ones) look great, but only fit a specific body shape - much like a helmet fitting.
I love the look of a set of Cobra seats I saw in an e46, but they were too tight on the hips and too loose on the torso, I even toyed with a set of Tillets, but didn't think they'd be particularly good for a 500 mile commute each week, or the 700 mile each-way trip to the Ring.
You'll need to check the height & width of the seats as the Z4 cockpit isn't as spacious as an E46 and most seats are a very tight fit - especially where the 'ears' meet the door or B-pillar.
IIRC, I had to by specific Z4/e92 floor mounts (maybe the floor mounting points are offset compared to e46/e36?) - but the rest were the same Recaro part numbers for mine.
My Pole Position ABE are 580mm wide at the ears (which catch on the door), is 850mm high, and has a 430mm wide seat:
The Bimarco Futura seem to be wider (595mm), taller (940mm), but have a narrower seat (400mm):
Without all the mounting gear (floor mounts, sliders, seat-belt rail), the extra height might not be a problem, but in the Z4 world every seat fitting is an experiment as most have never been tried before (part of the reason I went for the Pole Position ABE, as I've seen it in a couple of Z4s).
This is the 'extra' kit I installed in mine to make it useable:
As you can see, I've got mine as far inboard as the floor mounts will allow (an adjustment that these floor mounts allow, but your's can't), and it still hits the door - but I can't go any further inboard as it's already hard up against the transmission tunnel:
Are you planning on using just harnesses, or have you worked out a way to mount your seatbelt & pre-tensioner to these?