I want to put wheel spacers on my car to make it look better, but don't know how much of the wheel spacers I should get, any ideas?

 

Well .....first consider the negative side to wheel spacers when using them for looks. Then to*find the correct thickness you need to go measure the spacing of the wheel well and clearance on the front with full steering left to right and anything else that may get in the way?
Generally speaking and I do mean generally, 10mm (safe ) -*25mm maximum hub centric machined wheel spacers should give you what you are looking for with out clearance problems using STOCK MAZDA OEMs
Using wider spacers will cause all kinds of concerns!