I used to make frozen berries in jelly a lot. I would tip a large quantity of the frozen berries into a serving bowl, make up a pack of sugar free jelly crystals with about three quarters of a pint of boiling water (stirring like crazy) and pour this onto the berries straight away, stirring them round a bit so they were separate from each other, and pushing any that floated under the surface. I found the jelly set almost instantly round the fruit and because the berries were coated with jelly they didn't leak much juice as they thawed out - and they thawed almost instantly too!
Sorry I can't answer the Muller Light question but it's probably in the recipe section somewhere.