Have you tried putting a selection of food out for him to feed himself with at his normal feeding time. Things he can pick up, strip of cheese, bread sticks, cucumber sticks and other bits and pieces. If you leave him to it, he might try a few bits.
How about you start by mixing a little something else with the foods he will eat. Like a tiny bit of purreed fruit with his porridge at breakfast but only a smidgen so he hardly notices and then increase it slightly each day. Or a vegetable into the fruit pots, purreed carrots or sweet potato would probably go well.
I'd definitely drop his milk, as he's probably still feeling quite full from this. My 12 month old has only been having 2 bottles (totalling 12oz a day) since he was about 9 months.
Hope others can offer better advice xx