What about Shetlands? That's what we have and they are lovely cattle. Small, thrifty, hardy and docile. Milky and good mothers. Remember, they were developed to share the house with the crofters, so docile is good
We just put our first bullock away; we got 163kg beef back (well, 158 back and 5 to a local piemaker) and it is fabulous. He was 28 months; never seen a bag of feed; wintered last year on straw and a licky bucket and finished off grass.
If you search in the Diary above for cattle, you'll see more of our experiences. All I woudl say is that Shetlands are very rare (not expensive, just rare) so if you do decide to have them, please breed pure and help look after the breed.