Having moved up to a travel trailer after 14 years of a pop up, I know what you are doing. Sorry, but what you stated you wanted and 20 feet isn't happening. In terms of quality, they are all in the same ball park. Not great...unless you really want to spend some money. A quality improvement will cost you around 5-7K over what a "regular" one will.
As others noted, your tow vehicle will determine your trailer limits. Speaking from my experience moving up, we went to a 22 footer Aspen Trail old 1700BH and it was nice including a 41 inch bottom bunk and all the amenities without bells and whistles (e.g. manual hot water heater, had to add front stabilizers etc. We ended up going to a 27 foot Aspen Trail 2340. The big draw was a private bedroom, full bunks and the slideout. They make for a great deal of roominess vs regular ones.
Also remember, there are two widths out there. There are 7 foot wide and 8 foot. I prefer 8 feet because of interior room... IF, I was moving from a pop up today, I would consider an Aspen Trail 1950 BHS. You aren't used to room so not having a slideout won't bother you and it is 8 feet wide so it has a "real" dinette vs a 7 footer. And they have put a few bells and whistles on now like auto stabilizers front back I believe. It has "full" bunks AND an outdoor kitchen. It's still pretty basic, but about right. It is imho a sweet spot floorplan. Quality is not the best but about average for the majority of units out there these days... And you can get one for about 21Khttps://www.dutchmen.com/product/aspen-trail-le And you will find if you sell your pop up, it will get more than you expect... I'd recommend you sell it yourself vs trade.