Do you currently have mice? If so, humane live traps would be the best solution. Remember when you trap them, to bring them a minimum of one mile away during the evening so they can find their way into a new territory. If humans live traps aren't available, instant kill ones would be the kindest option. You can get galvanized steel mesh at many hardware stores as well as online, I'll leave a link below. Make sure the holes are 1/4 to 1/2 inch spaced max.
https://www.amazon.co.uk/gp/aw/d/B00...TdL&ref=plSrch
https://www.amazon.co.uk/gp/aw/d/B01...rds=steel+mesh