Okay that make sense! It's a series 3 88 station wagen, there isnt really a budget but cheaper the bettet

I do tow with it already! I have road tyers on her at the moment but i am looking to get another set to be off roads ones! Which ones I don't know yet!
Do you think if I get new suspension and shock absorbers for the back that would stop the sag?
Tbh sagging stock springs is reasonably rare unless they have been worked very hard.
So in answer. Stock new springs should revitalise it and make is usable for most uses.
There are different spring packs however. Usually dictated by the number of leaves. As a rule the more springs the stiffer. Stiffer springs will generally tow and haul better, such has having 4 adults in the back. But will ride harder when empty and won’t flex as well off road.
A Station Wagon also weighs more than a truck cab, specifically the rear axle loading. So consider this when buying.
Stock springs should allow 7.50 x 16 or 235/85R15 tyres to be run without issue. Which is normally sufficient for most needs.
The main issue with leaf springs is they will stiffen up when left idle as they will rust solid. Regular use and carrying heavy loads helps avoid this problem.
There are also parabolic leaf springs available. These were first introduced for Land Rover on the 101FC. They use less leaves and the leaves aren’t in full contact with each other. So they don’t then to rust solid.
Parabolic springs should offer a much more compliant ride. However as a trade off may induce more body roll. Because they are softer and allow more roll. They can also tramp a little off road more easily. Also be warned, the quality of parabolic springs used to vary a lot. So do some research before buying. Also understand the different spring rates. Many people buy multi leaf parabolics which are very stiff. These may end up riding harder than stock leaf packs.
Worn bushes on the springs, hangers and chassis can all cause issues and are worth looking at replacing.
As for lifting a vehicle. As said, I suspect you don’t need too.
But you could fit longer spring hangers/shackles. Such as the military ones from a 1 Ton 109. The problem here is it will change the pinion angle of the diff and may cause problems. But might not. The 109 has extended spring mounts at the other ends of the springs as well as the longer hangers. You could fit them too, but will be custom and require welding.
You could fit longer/stiffer springs. This will give a lift too. But too much and you may also encounter diff pinion angle issues. And may end up with reduced travel off road. Most parabolic springs will give a mild lift in this way.
Other ways of lifting could include performing a spring over axle lift. The stock leaf springs mount to the bottom of the axle tubes. Many other vehicles, including latter leaf sprung Land Rovers mount the leaf spring on top of the axle tube. But this will require other custom work to achieve.