I hope I'm not derailing, but I think this conversation would be beneficial to the lurkers and those in early-wardrobe-building mode like myself. I, and my pockets, LOVE the idea of being able to find a navy suit that can double as an odd jacket when switching the pants. The tough part about that is how one jacket can pull off those two different looks and do so successfully. Drawing on the principle that a suit can be dressed down easier than an odd jacket up (which I still agree with), I would START by trying to find a suit that would look fine as a suit while having the below blazer properties I've sketched out:
Solid navy, SB, notch lapel, dual vents, 2 patch pockets, horn buttons, 3 or 2 buttons, soft shoulder, NOT worsted.
The only thing that sticks out to me is the patch pockets and being not worsted. Finding this illusive suit on the cheap is tough. I think I'd have to cough up the dough and look towards someone like Kent Wang to make it up in something I can afford. I don't know how I feel about my first navy suit with notch lapels having patch pockets.......
Hmm. What do you mean by not worsted? A blazer should be made out of a worsted cloth. Were you thinking of a woollen flannel? That would make for a very odd blazer. Just wrong, actually. If you want a cloth suitable for a blazer with more texture, checkout hopsack.
You will not find a RTW navy blue suit with patch pockets. Just isn't out there. A three-roll-two front is also rare. If you are stuck doing RTW, look for a navy suit with double vents with flapped pockets. Then, if the buttons aren't so already, switch them to brown horn. That will suffice.
Otherwise, the only way to get a BlazerSuit like you describe is to get it MTM or bespoke. Don't worry about that if money is an issue. The flapped pockets will be fine.
Uhh, I'm sure there are colors and patterns to avoid that wouldn't generally apply to all shirts. At first blush, I'm not sure why you'd think about a buttondown-collared shirt that much differently on account of the collar alone. I guess I'd avoid white.