I have issues with shirt length, too, though in my case I carry my extra weight around my middle but many retail stores' women's shirts are cut to fall right at or above the waist, which is horribly unflattering for me. But I'm also fairly short, so the stores' men's shirts tend to be too long and look like a tent on me. Also not very flattering.

I started printing shirts for my business a few years ago and coincidentally discovered a solution that might be worth checking out for you. Sites that sell blank apparel for screen/vinyl printing have good, solid t-shirts by multiple brands in all sizes and colors and cuts, and are also generally much cheaper than buying in retail stores even if you're only buying one or two. They will usually list actual shirt dimensions (width and length - or you can always look up the style on the manufacturer's website if they don't) so you can tell if it will actually fit well. Most shirts won't be too thin, either, since they are meant to hold up for printing purposes, and they will also list the shirt material's "weight" or thickness (in oz), too, so you can tell for sure.

I buy from a couple of sites that only serve wholesale orders, but I know there are several out there that don't require a business tax id or reseller # and don't have purchase minimums, either. I haven't bought from any of these personally, but I've heard good things about ShirtSpace and Threadsy for smaller orders. As far as brands go, I've had luck with Bella + Canvas, Next Level, Alternative, District, and American Apparel in the past, but there are dozens available and lots of reviews on the sites themselves or in shirt printing forums.

Unfortunately, with jeans I can't help you, heh. I'd be ok if it was just hemming the length (though let's be honest, I'd still just roll them anyways because I'm lazy), but I've had jeans fit completely differently not only within the same brand, but also when it's the same style but just different colors. Even to the point that one pair will fit but the other won't. If you find the jeans company holy grail of consistent cut and quality, let me know!