I've recently moved towards freezer bag cooking and in the UK was using 'store n pour' bags like these -> http://www.lakeland.co.uk/10914/1-litre ... Sauce-Bags.
They have several advantages over normal freezer bags; you can pour boiling water into them and they don't melt, they have a wide base so they stand up on their own, and the ziplock seal is very secure.
I've tried googling a load of different terms and looking in shops, but can't find anything similar here. Does anyone know if it exists?