Native 4K with good IQ @ something like 55" is a very nice upgrade over 1080p. You're seeing more granular detail at that point which previously might have looked more like noise. Combined with HDR, those two make a pretty notable upgrade on a new TV. Assuming you're choosing a set with good HDR brightness and response time, you can find some value-priced options for exactly that (including the bigger size).
This said, the option of higher refresh rates and VRR will be something you may want to factor in for this gen. This will up the price of what you're looking for, but especially if you're happy with something like a good 1440p display w/ 120+hz/HDR/VRR around 32", there are some completely reasonable options out there.
Remember that HDMI 2.1 will only matter for you if you're planning to be running 4K @ 120hz, and a 2.0 port will run fine at something like 1440p @ 120hz, or 4K @ 60hz. As others have mentioned, rtings.com is a great resource for both individual device reviews, and also contextualizing what some of these features/qualities look like.