I discoveredTop Shop Leigh, and stuck with them, as they do 34 length. However, since losing weight too quickly, even they're bagging within an hour. So, I've started over again. Standard Primark cheapies are fine, H&M a bit better, River Island fit me like jodphurs (sp) - not good. TK Macs have yielded a decent pair of 'butt lifters' - one of their own pretend brands, I suspect. But the best so far are some G-star,xproper jeans, from the charity shop. Lowish waist, which I find more flattering on my no-bum, feel like decent quality.
As for keeping them black, I'be gone back to good old Dylon. Chuck one in the washing machine, with the worst offenders, every 6 months. I've done this since I first started wearing black skinnies, in the 80s - they were 51 States, from Leicester market, back then, and the bottom 6 inches had to be stitched closed, then ripped open again to get them off! They were sold by waist size then, too. Oh, to be able to just ask for some 24s, hand over my £6 and go home happy. Sometimes, I think there's too much choice now.
But, yeah, black Dylon machine dye.