What stops commercial ice lollies from being rockhard?
If they are rock-hard, they need more sugar (or you're one of those people that use artificial sweeteners and they don't have the same effect that sugar does.)

About 30% sugar is a typical proportion that works - feel free to experiment. i.e. mix 300g sugar with enough water and flavoring to make 1 liter of mixed solution. If using juices, calculate how much sugar they contribute from the label information and add enough more sugar to reach 30%

Pectin can also be helpful. You need things that interfere with the size of ice crystals. Jam is one way to get it, (and some sugar - again, read the label to find out how much) or you can get the pectin made for canning your own jams.