Changing leaf springs is surely the best way. I don't know what dampers you have, if they are standard, why not replacing them with adjustable dampers in a first time?
On my 2005 PLUS 4 when I have changed the rear dampers with adjustable ones, big improvement, no bottom out after.
Testing the previous standard ones (35 000 miles) they are like a bicycle pump.
If your dampers are not good or enough efficient, it does not help. They don't have the same function as the springs, but it could improve your concern. Not difficult to change,not too expensive and in a second time changing the leaf springs?
It could be a good investment for the future even if you change the springs.
