Pete,
you can sign up for a free selling manager on Ebay. https://pages.ebay.co.uk/selling_manager/
Once you are using it,
open up your 'my 'ebay' page.
3 tabs on left> 'activity' 'messages' and 'account'
>click 'account' tab.
under 'selling manager' click 'awaiting postage'
this brings up a list of ended auctions that have ended and been paid for, awaiting posting.
You can tick a listing and choose 'e-mail' buyer, opens drop down list of different e-mail templates (which you can edit). Select 'dispatch notification'
thats it, your done.
tips on using free selling manager here https://pages.ebay.co.uk/selling_manager/faq.html