Ultimately, I think you have to make a choice between portability and tone. The more portable the less like a URB. I've heard good things about the Merchant, Messenger, and BSX basses but haven't tried them myself. I've also read that the Yamaha is well made and feels like an URB even though it doesn't sound too much like one. The typical complaint about the Yamaha is it's kind of pricey for what it is.
I have an Eminence and NS Design Omnibass. I vastly prefer to play my upright, but I use the Eminence when I'm flying or going to a local gig when I'm concerned about the load in or space on the bandstand. I use the Omni when I'm flying on short trips, just a few days and don't want to have to fuss with disassembling and reassembling the Eminence nor check a bag.
For me, I find the Eminence feels just like my URB to play, I make no adjustments. The action is slightly lower and the string tension a bit lighter but neither distract me in the slightest. I'm not generally thrilled with its tone which I hear as lacking depth and kind of muddy. The nice thing about the Eminence is I don't need an amp to practice in a hotel room. I can hear it fine but it's not loud enough to bother anyone else.
The Omni is not very much like a URB in terms of sound, but I like it quite a bit for a very portable practice instrument. It doesn't really sound like a fretless bass guitar either to me. Maybe more like an electric cello? I think it's a unique sound. It doesn't feel much like a URB even if it weren't a much shorter scale, because there's no neck heel or shoulders. Some players would call that an advantage because it makes it easier to play - you don't have to use thumb position to play above the octave - but it might require some adjustment if you're used to relying on the neck heel. I use thumb position anyway and I don't miss the heel. I find I hear the Omni fine in a quiet hotel room without an amp and it bows very nicely. The string tension is very light and the action is pretty low, but raised to its maximum I find I can still use a proper right-hand pizz technique on it. I use an endpin because I like to stand while I play and the endpin is a lb or two lighter. And, with the Omni, I carry it onto the plane.