NIHBS has been promoting the development of a native bee which can coexist with the varroa mite more successfully than at present.
Some colonies of bees deal better with mites than others and in part this has a genetic basis through inherited behaviours such as biting and grooming of mites, and an ability to detect and uncap cells which the pupa shares with one or more mites.
Counting mites on the bottom board under the open mesh floor is very unreliable as an indicator of mite infestation levels.
A more accurate way to count mites is to take a sample of 300 bees, roll them in icing sugar and count the mites which drop off.
There are instructions here, including a link to a video.
You can purchase a shaker from Mill Lane Beekeeping, contact details here.
There is background information on the Ireland Varroa Monitoring project here.