I've bought four used sofas in the past as well as several used upholstered chairs and they were all fine. They weren't great . . . at all . . . but they were fine. The price was right.
However, I've also been bitten by bed bugs in the past in two different hotels . . . I'm highly allergic and it is a really terrible experience. The second time I got really paranoid I might have brought them home with my luggage and I ended up paying for "bug sniffing dogs" to canvas my home. I didn't have bed bugs, but it's such a bad experience having them that I was just happy to write them a check anyway for the sense of relief of being sure. Some people aren't allergic and don't even know they were bit. Go figure.
So, I've decided no more super cheap hotels and no more used upholstered furniture for me because I can't really treat it to be sure there are no bugs.
In this instance I think you might be living up to your name, pound_foolish. A sofa is not meant to last 19 years and new sofas are just not that expensive. If you had a sofa for 19 years, then I feel like you paid your dues and you've earned splurging on a new one. If all you need is one sofa, then look at the more reasonably priced retailers (places like Rooms to go) and discount retailers (places like Big Lots) and pick something you actually like in the style and fabric you prefer. If you live in the Denver area, then go see Jake Jabs at the American Furniture Warehouse for 1000's of cheap but new sofa options . . . lots of places have a similar giant discount furniture retailer. Often the sofa itself is pretty decently priced but what they really want you to do is spend another $300-400 on the matching ottoman and another $600 on the matching chair and another $XXX dollars on the tables and lamps that go with the set . . . so resist that: just get the sofa. Realize that in 4-5 years when you move it will probably be time to buy a new one anyway, most likely, and you can sell it if it doesn't fit in your new space. Labor Day sales have already started in many areas, after all. I'm not saying spend $12000 on a sofa, but you can get a really nice new one in the triple digits if you look.
Also, measure your existing space, then go to a store and sit on the sofas . . . it's amazing how differently sized they are, and how one that is comfortable for one person might be very uncomfortable for someone of a different height. Once you really know exactly what dimensions are most comfortable for you, then you could even buy one online, but there's no substitute for sitting on a bunch at the store.
I'm going echo Clintin Kelly (of What Not to Wear fame) and say buy something now that fits the size you are now . . . don't wait for "someday" to get something decent.