Lin try making your own mashed veges that are not as smooth as purity, but still not big chunks so that he can get used to more texture. All the yellow veges (butternut, gems, etc) freeze well, so you can make lots and freeze portions. If he really likes the taste of purity you can try mixing some in at first so that he gets used to new tastes. Then you can start making vegetable "stews", eg saute tiny bit of onion, add sweet potato, butternut, baby marrow, tiny bit of good vege stock and add enough water to cook veges, but not so much that you have to drain the water off. Because we're vegetarian I also add things like lentils, quinoa and beans. Then mash it up and try giving it to him. I sometimes stir in some grated cheese or smooth cottage cheese, which my son likes. I always make quite a big pot and then freeze the left overs in portions in small tupperwares that take 5-10 mins to cook from frozen on the stove.
It may take some time for your LO to get used to new tastes and textures, so try and be patient and persevere. Good luck.