Yep you can just get a unitard from a dance store or a morphsuit (I find the unitards to be of better quality and not much more money). Then I would personally make a template of the blue design and have someone paint it on using the template. Alternatively, pin on an iron-on piece while wearing the suit, take it off, and then carefully iron on the piece (though heat can damage spandex so I wouldn't recommend it), or the best idea would be to make the blue piece out of spandex, pin it on while you're wearing it, and then sew it on as neatly as possible.
The source costume appears to have the blue painted on. The belt, forearm armor, and right shoulder piece look to be made of EVA foam, which wouldn't be very difficult to do at all.