The most aero looking mirrors I could find were these:
https://www.pegasusautoracing.com/images/L/5168-001.JPG
170 dollars :/
They also have a rectangular one, which I can't really tell the shape of but it looks to be a little longer as well. It's cheaper too, but still expensive.
Re: jedi sol that looks pretty good! The clips are a good idea for the front. The rear suspension would probably knock your drawn diffuser off and the muffler would melt the rest, but it's okay, just a crude piece of metal attached to the muffler would be fine.
After some more thinking I realized I should probably just ignore the underbody and use an aftermarket front splitter / airdam, because I still have faith someone is going to build a nice small midengined 2 seater which I will enthusiastically trade my BRZ in for. No reason to put all that effort for the next owner in a few years.
When the dream car comes, I'll definitely do a full bellypan.