My lil Romeo is picky too! I've tried various types of foods too. he won't eat the raw diet, so thats still in my freezer, just taking up space!
I've recently tried Life's Abundance, with the recommendation from YT's own Linda of fufufashions, and he's been eating that. The kibble pieces are a little big for him, so I cut them in 3-4 pieces, which is a lot of work, but anything for my baby
It also came with a daily supplement, which has a lot of the vitamins/minerals they need. I usually give him half a tablet a day. I also boil chicken and rice for him in case he decides to not eat the dry food.
Sometimes give him fruits/salads chopped up. He's take that down especially if thats whats I'm eating it! I've noticed even if his food is more delicious than mine, he still wants what I'm having! Sometimes I act like I'm eating his kibble, and he starts eating it! But I think he's catching on to that
Keep us updated! Good luck to you. Just remember to be patient and what works for one yorkie mommie may not work for the you! Keep trying! I like the cottage cheese/yogurt idea too and may try that soon.