I'm a size 20/22 and have struggled for ages to get tights that fit well,dont fall down, cover my bum. found a pair the other week that do this so thought I would share! 
primark 100 denier tights are brilliant. I haven't had to pull them uo once and they have a nice amount of "give" too. (dont feel so stretched they'll rip. )
On the other hand, tights from "yours" were a complete nightmare. Honestly couldn't walk more than three steps without them falling down.
(If only I could now solve my nice plus sized pants issue I'd be happy)