I know it's little comfort, but my DS (just turned 6 months) is an awful sleeper. He was EBF for the first 3 months, mix fed for the next month and completely on formula at 4 months.
And switching to formula did not affect his sleep a jot
I started a few spoons of puree last week, and he seemed to sleep a bit better. Then, last night, he slept 6.30pm - 4am
Up til then the best he had ever done was 5 1/2 hours, and that was so so rare. But he hardly ate anything yesterday, so I can't claim he was so full of food he didn't wake for milk.
I honestly think he is just taking a while to learn to self settle (he co-slept for the first 3 months, as it was that or not sleep at all. Not ideal, but you do what you must, don't you?) and be able to get into a deep sleep.
Am praying he repeats it again tonight and that this is a step forward. Even if he doesn't, I know that he can do it, he doesn't need feeding in the night, and he will eventually get there.
I know that's not the advice you wanted, but imo, it's just a question of waiting :)