The stock appearance of a WH is racked down at the front, If it sits level or down in the back then the springs are compressed (happens to most WH's that tow).
If you use a tape measure and measure from the centre of the rear wheel cap straight up to the guard it should be about 495/500mm in with stock suspension. My M/D OME sits at 540mm.
Getting standard height springs isn't easy other then factory. Most offer lifted only.
If you fit raised springs to the rear only you won't be happy,
If you fit heavy duty raised rear springs you definitely won't be happy.
If you don't want a lift at all I suggest sourcing stock Commander rear spring for yours, they have a slightly higher coil rate and will sit right with stock front suspension.
I don't recommend fitting H/D rear coils just for towing, they ride really harsh when unladen. I use M/D and it tows my van nicely.