Really, it sounds like you will be fine with any type of GSD you get as long as you are buying from a reputable breeder who puts temperment first and you are very honest and clear with your goals and expectations of the dog. As a general rule, working line will have higher drive, but so much also depends on the individual dog. I don't think it will matter one way or the other for you as long as you don't overstate what you are wanting from your dog.
Are you fluent in Slovak or Czech ("from" could mean any number of things...you moved to the UK at 6 months or 26 years of age)? Obviously having no language barrier will make things much easier. There are a lot of good GSD breeders in Slovakia and the Czech Republic--you should not have a problem finding one.
I got one of my dogs from Aritar Bastet in the CZ and I was very happy with the process and am very happy with my dog, although I wouldn't consider him a "beginner" dog (but that is not what I wanted!). But he's got a great overall temperment (ie not dog reactive, social but doesn't act like a lab, etc) so as long as you are clear with the breeder as to what you are looking for I think he delivers nicely.
Here is the thread for our BH video that we recently did
Medo Aritar Bastet - BH Video