My sun conure has an aviator harness which he hates. But between a flight suit and harness, I still think the harness is superior. It is less restrictive.
With regards to using the flight suit as some sort of diaper, I highly advise against it. It is unhygienic for the bird, with stool making constant contact with its cloaca. This will undoubtedly cause health issues down the line. I've also read accounts of more serious long term complications when birds decide to hold in their stool (because they feel uncomfortable letting it go with the material being so close to their rears). Pressure will build up in their rear from the stool not being released, and cause a distended/inverted cloaca. This is extremely painful and harmful for the bird.
A better way to improve poop clean up is to train the parrot to go on a designated spot. This could be a poop perch with paper underneath, a trash bin, toilet , napkin, etc. It is very, very easy to train them. It's the first trick (dare I say one of the handful of tricks) that my parrot learned. Just wait till you know the bird is ready to do their business (every 15 to 25 mins for most medium birds), then take them to the spot. Say 'POOP!' or whatever catch phrase you wish, while the bird is pooping and immediately right after. Reward with lots of verbal praises and scratches. In time, your bird will associate the word/phrase to the act of pooping. Once trained, all you need to do is say your catch phrase while at the designated spot and your bird will go. Additionally, I let me bird know that pooping on me, the carpet, the couch, the computer chair, etc. are NO-NOs. I tell him 'NO' firmly and shake my head / look disappointed. Lastly, avoid food rewards because birds can get obsessive and might intentionally hold / push poop out just to get one. This can also cause problems with their cloaca.
Hope this helps!
cute. 
