Changing the springs on your old car probably altered the rebound frequency, to take it out of the zone that affects your missus, so it's not necessarily more ride height you need .. just different characteristics for the suspension.
Longer springs isn't an aftermarket option, as far as I know. If it was me I'd get some new and improved dampers.. something like Bilstein kit... particularly at the rear.
If your standard dampers are a bit weedy, then even new standard dampers might improve things... but some adjustable Bilstein etc. would definitely be different. Improved damping will change the "float" of the standard suspension and bring the movement under control quicker too.
You could also look at different tyres. If "hard" suspension is more of a problem for your missus than the up and down movement, the you could go up an aspect ratio on the tyres and that would again change the suspension frequency a bit. Car might look strange and check how much clearance there is before the front tyre touches the underside of the damper.
Otherwise... you could try "white man medicine"/placebo effect and fit one of those lightning conductor things (you may need to ask your dad) to your rear suspension beam, to earth the car over bumps.
When I was a car-sick kid, my dad fitted something like that to his 132 (you may need to ask your dad) and it "worked" on a long continental road trip. When we arrived I noticed the thing had fallen off (probably on the channel ferry loading ramp) but thinking it was there all the time, made me completely travel-sick free.
Ralf S.
