Wholesome Breeding of Sound Miniature Cows

I am struggling to find breeding techniques and information on how to breed efficient sound miniature cattle. And it seems I must embark on this journey towards breeding a smaller cow. Much of what I find, even in permaculture sites is breeding for exploitation, economy, convenience or cuteness. I have yet to find anything on sound physical attributes and propositions. I have the basic understanding of good posture, quality udders, hooves and temperament. But I haven't manage to find breeding techniques and strategies. My region used to have what is now considered a miniature cow, but that was all but forsaken to get a bigger high producing cow. Now the breed is a blown up version of its former vigorous self.
I have to make decisions like should the mother be larger and the miniatureness be brought in by the father. What range of calf size can I work with. How to make the size proportionately smaller, not dwarfed, deformed and/or stunted like I see in many recently marketed miniature cattle. Does anyone know of sources or breeders or anything?
Please understand, I am not looking for unsolicited opinions or remarks from people who have chosen something different and feel they need to defend themselves or their reasoning/theories.
I need sound, hardy, dexterous, light weight, strong, efficient, intelligent cattle that can fend for themselves when they are released in our large free grazing mountainous and swampy areas. It existed here once, I need a roadmap back to it.

I have communicated with a couple of people who claimed to breed miniature. One was too far for me to visit. The other shut me off by telling me he did not have any at the moment.  Lacking other ideas, you might want to check with a vet and a university.

Why not pick one of the already existing hill breeds like the highland, they are already common in Norway and already bred. or Dølafe?  Both breeds are small (under 500kg) and bred for rough grazing, belted galoway would be another choice as well if they are avaliable. if there is something you don't like about them then start with them and try to breed it out.

Thank you the responses. I have contacted vets; unfortunately, the focus in Norway is breed bigger for production profit. There are breed groups, but outside ofthay, they don't know more about breeding for improvement not geared toward conventional production. Unfortunately, none were particularly knowledgeable in going in any other direction (pout). I may have to wait to see if I can get a smaller framed cow and work from there.