At a minimum, I would keep them confined to a run with a solid roof. That's a pretty standard recommendation. Wild birds can still perch on netting supports, above your birds. I wouldn't have perches for wild birds, like trees, right next to the coop, myself. No free ranging. Think about how to not potentially track disease into your coop or run on your footwear. Dedicated footwear or disinfecting foot baths at the door for your shoes are good ideas. You could also build your coop with access doors, so you can reach in to do more of the chores, instead of walking in.
Beyond that, if you take the very best care of your chickens, they will have stronger immune systems. A good diet and as little stress as possible keeps chickens healthier. Things like inadequate diet, running out of water or being bullied in crowded conditions, stress chickens and that suppresses their immune systems.
I'd be looking for recommendations in the country you're going to and also at some of the recommendations in the UK or Europe.