[boracay]

"a single €0.99 sale in Estonia"

Would of course be done through a service. Maybe it's time for these "innovative" payment processor to actually be innovative and provide this service.

"£81,000 threshold applied to the new arrangement"

It can't apply to the new arrangement since you are now paying taxes in the customers country.

It seems that you would just either do your local sales as before and your international sales through a service or start two companies. That why you should be able to keep your threshold for domestic business. (Don't quote me on this though since I'm not in the UK)