I've been using hollowbody basses to mimic uprights for decades. My current favorites in no particular order are a Gretsch Electroline G5442BDC, Epiphone Jack Casady Signature, and a Hofner Icon Club Bass. Many will get you there if you use flats (I use Labella nylon tapes) maybe a mute, but that's just part of it. I found that adjusting my technique, plucking position, note selection, and mindset went a long way getting me more into the upright-esque realm.
One of my favorite upright simulators is the old 18" scale Guild Ashbory (now available from DeArmond/FMIC). I've used an Ashbory since the mid 90s.
I've just recently purchased a Gold Tone MicroBass which uses "rubber" strings like the Ashbory but it's a 23" scale small acoustic guitar type design. It also appears to be a promising upright simulator. There's also the Kala U-bass which is a 20" scale ukulele style and also uses "rubber" strings. Kala also makes a solidbody version using the same scale.