I'm not very familiar with Prussia's character but from what I know this
is Himaruya's official chibi drawing of Fem!Prussia.
And you can click here to see an accurate cosplay representation of the outfit.
However be careful with what you choose to cosplay in! People can definietly tell a closet cosplay vs. one that took effort/time. But of course people make different variants that look amazing! And I'm sure if you put in a good amount of effort you will establish a very nice costume!
If you're looking for someone to go "wow!", make it accurate and recognizable. =)
Prussia's eye color is certainly a key factor but if you don't get contacts that's fine. My aunt is an eye doctor though and suggests you get your eyes fitted for contacts at a clinic and not to order them online since technically it's illegal to purchase contacts w/o a doctor's consent but contact salespeople have found loopholes and whatnot.
And I just realized this thread is almost a year old, OTL.