Kind of chancy 2nd hand, but if you buy from a breakers they will change them if they're not right.
I've bought them once before and they were fine.
Originals are definitely better to take a chance with though, and it is possible to get ones with lowish mileage on that will last you a good while.
Unfortunately new ones aren't cheap, same as the rear shock too.
Just need to keep an eye out for the bargains, they are out there if you persevere.
Regulars on here will know i had major problems years ago with juddering up front, and i replaced nearly everything, and my last final option was to change my braided brake lines and it turned out that they were the culprit.
Still reckon that if you keep bleeding your brakes then it will improve things though.