My favourite bass of all time is a Sadowsky RV5. Unfortunately it weighs 9lb 7oz (4.4kg). That's not a lot, but my back hasn't been able to take that weight for a couple of years. I work out, and while I'm fitter and healthier, it doesn't put the clock back in a way that will satisfy my back.
Last year I bought a Sandberg TT5 SL (6lb 8oz), Ibanez (7lb) and Cort (7lb), and I'm still trying to work out which will take over as my #1. They are all light, feel good to play and my back is happy with all of them, but they don't have the sound I'm looking for. I bought a Sadowsky preamp pedal which only gets me half way there. IMO the Sandberg is the best of the bunch but I'll need to replace the pickups. Decisions, decisions!