If you are willing to carry another bass in addition to an electric bass (if that's what the gig calls for), I would go for a semi-acoustic bass. Slightly bigger body than an electric, but the same scale length and overall feel. They do have fretted and fretless models. Obviously, if you go fretless with flats, you'll get closer into the upright territory. There are the three that come to mind, depending on your budget:
Rob Allen
Probably the cream of the crop in this type of bass. There are different models and they all sound great from the videos/demos I have heard.
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New ones can be pricey, but if you can find a used one, you might be able to get a deal. I had an (older) one and it really did the upright thing really well.
Sire GB5
This would be the budget version of the Godin and appears to be similar to the older models.