1999 E300 Turbodiesel rear springs

[GREASY_BEAST]

I'd like stiffer rear springs and shocks on my W210. I sometimes tow a trailer, and I often load my car down with hundreds of pounds of tools, people, luggage, etc., and I'm getting tired of bouncing off the bump stops on the highway.

I've seen advertised various places "HD rear springs" for a W210 (like this). I just checked my car and it has rear springs marked with 1 green and 1 yellow stripe. The EPC lists two rear spring part numbers:

210-324-32-04 -- 1 green/1 yellow (mine)
210-324-33-04 -- 1 yellow/2 green (HD?)

Is the 210-324-33-04 an "HD spring"? If so, is there some corresponding "HD shock" to go with it?

EDIT:

Did some searching on the Lesjöfors website. Looks like there are indeed two "reinforced version" rear springs springs. One for trim level "classic/elegance" and one for trim level "avantgarde". According to the Bilstein website, MB PN 210-324-32-04 corresponds to Bilstein PN 36-225927 which is for trim level "classic/elegance". So I assume that means I should go with the Lesjöfors 4256843

Bilstein lists a PN 36-226030 which is a "heavy duty" rear spring but it lists trim level "avantgarde".

So.. Is the "avantgarde" vs "classic/elegance" distinction important? I'll look around and see if I can buy a set of those Lesjöfors springs, I've had good luck with Lesjöfors in the past. I guess I'll put on some Bilstein B6 shocks too and call it a day?

EDIT2:

Found them on Ebay. So I think the plan is:

(1) Put Bilstein B6 shocks on all 4 corners
(2) Put Lesjöfors PN 4256843 on the rears
(3) Order some spring shims of various thicknesses to make the car level out right
(4) Get an alignment done afterwards

Just looking for a sanity check.. does this all sound like it'll do the job?

EDIT3:

I've only been able to find rear B6's in stock in the UK, Netherlands, and Germany, and on Amazon for $230/ea... Now I'm tempted to just try the HD springs with the stock, probably original shocks that are in my car currently... $460 for rear shocks is way too steep.

EDIT4:

After heaving on my front and rear fenders a bit I've concluded I could use new shocks anyway, which makes sense given the car has 100k mi and they're probably original. B6's will be $460 + $248 = $708. OEM B4s will be half as much -- $354. The HD springs are $62.50 each. I'm going to try the HD springs with OEM B4's and hope the car doesn't buck like a mad steer. If it's too awful to put up with I'll just put the stock springs back in it and eat the $125.