This is all hearsay, but make of it what you will.
The Herdy's traditional landscape is the Lake District fells - which are more stony / rocky than boggy / peaty. It's a sheep that is hefted, ie it is used to having a territory that it and its daughters graze.
Hefted fell sheep tend to want to be high up. Certainly if you buy draft ewes from a hill farm, they seem to always find the highest land in the terrain you offer them!
I haven't had bought-in hefted sheep for more than a season, but the ones I bought in for the moorland farm just before I left there didn't really settle. The ground was different to what they were used to, the forage ditto, and the land was not high enough for them. (They were Swales, but I think the same would apply to adult Herdies.)
People say that Herdies have great feet - in their natural habitat. Anecdotally, their feet do not do well on wet boggy ground. (If you want good feet on wet ground, get Exmoor Horns.)
I do know of people with Herdwicks that seem happy on better ground and smaller enclosures, but I also hear a lot of people say that they're wild, need space and altitude.
Having said which, many Herdies in the Lakes are wintered for their first winter in-bye, so on lower, smaller enclosures.
If you do go for some, I would try to buy from a flock being kept on a similar system and terrain to your own.