I think there are a lot of great manufacturers here in America. Look for those that offer a lifetime warranty on frame and suspension - that is usually a good clue it is made well. 8-way hand tied springs are the gold standard, and sofas that feature that usually have quality construction throughout the piece. Some manufacturers do good sinuous springs, but some do not, so it's a little more iffy. I'm partial to Lee Industries and The MT Company and also love Carolina Custom Leather for leather pieces. These are what I sell so am most familiar with them. A seat cushion with innersprings will hold up the best. Avoid down wrapped unless you are okay with flipping and fluffing daily.

Some other manufacturers with good reputations are:

Hancock and Moore

Taylor King

Stanford

CR Laine

Huntington House

Thayer Coggin

Wesley Hall

I've personally had a Lee Industries sofa for 15 years that has been through a ton of moves and it is still great! All I've had to do is replace the slipcover. I also got new cushion cores, though I didn't need them, I just wanted to switch to something firmer.

You can find a retailer near you that can help from any of these manufacturer’s websites.

I love Pearson and sold it for years; also Wesley Hall. Sherrill is another I like and Hickory Chair. Do go to better furniture stores and sit on lots of sofas! Ask an educated sales person for as much detail on the construction as possible! A quality sofa that will last you many years of use will be a big investment, so take your time!

Look into buying a custom made sofa from What A Room, much higher quality than big box stores as they have 2.5 lb densisty seat cushions which apparently can last over a decade. So you will see much less sagging and wear and tear of your cushions over the years. Other companies like Crate & Barrel and Room & Board only uses 1.8-2.0 lb densisty seat cushion as it is much cheaper. Also What A Room allows you to customize a lot like their fabric, cushion firmness, size, anything really.

That "What a room" site sounds like a good idea at a more reasonable price ... BUT looking at the photos in the reviews on their site, some of the sofas that are supposed to be brand new, already have saggy and wrinkled back and seat cushions, like they are several years old. Buyer beware! Do your own research and definitely don't order a sofa/chair you can't see and test in person.