The most effective thing I have found for retaining moisture is pure lanolin. The exact company/product name is not that important, if it's pure lanolin it will work very well. You can either use the regular kind, which has a similar texture to vaseline, or "liquid lanolin". The latter is much easier to apply as it's not waxy or sticky, but it doesn't stay on your lips much longer than anything else will, though it still moisturises very well. I would recommend starting with the regular type of pure lanolin (such as Lansinoh) as, if you apply it well enough, you won't have to apply it more than once a day if you're careful with your lips.
I am currently testing whether or not it will heal the skin in the long term. It's not hard for me for to keep it up constantly though as it's by far the best thing I've used on my lips. A few very small lines have begun to reform on my bottom lip where there was just red raw skin after peeling before, so I am quietly hopeful.
As with most things, there is the possibility of being allergic to lanolin, so it's probably a good idea to test it on a small area of healthy skin somewhere else on your body first.