Yogurt is sweet which is why he likes it... the same with cereal puffs and things like that.
I am not sure what to suggest because I weaned early (the "old fashioned way"), I couldnt get my head around BLW... and Jasmine eats anything I give her.
Has he EVER eaten anything else? Im not sure what to suggest, other then cut out the yogurt and watermelon and offer veggies and fruit only... like the others said, perhaps not nurse him as much, its great that your still bfing....
Obviously you cant force him to eat anything, and year old toddlers can be picky as it is (this is also the time when they start learning the word no, and how to defy their parents... lol)...
If he isnt accustomed to eating 3 real meals a day already it may take some persistence. And it may be hard for you, but he is going to really start needing solid food. Especially the extra iron babies/toddlers need for proper growth.