Can't advise on bearmach springs, but have just fitted britpart yellow standard height HD springs to my disco. I can't really report on how they drive as I only finished changing the springs this evening, and haven't tested them yet, but in terms of ride height, the disco certainly appears to sit alot higher than it did on the old springs, and although I've read some horror stories about britpart springs, the end result is that the ride height at all four wheels are all within about 8mm of eachother. Of course the springs will compress a bit as they settle down, but I'm pleased considering the bad press britpart springs have. A worthwhile upgrade considering like yours, my springs were 18 years old, and have done 181K miles. They were definitely past it, and clearly had lost almost of of their rigidity.
Are you thinking of just changing the springs or the dampers as well?
The reason I ask, is that before I bought my springs I was considering leaving the dampers and sorting them out at a later date. In the end the guy at the shop, convinced me to get the dampers as well, and I went for terrafirma gas dampers, and boy am I glad I did. I must admit that driving away from the shop I had that sinking feeling where I felt I'd just spent alot of money that I didn't need to, but when it came to fitting the new springs, I took off the dampers, and 3 out of the 4 didn't come back out again once pressed in, so it's no surprise that my ride was incredibly bouncy. It was a bit of a bitch of a job to change all four springs, and I'm glad I did the dampers at the same time, so now I can relax and forget about it, rather than dread revisiting it at some point in the future.
I can't really review the springs and dampers I've fitted, but my initial impressions are that I'm very happy, and I would certainly recommend doing both at the same time, and not just the springs. Good luck.