Like you, I have weird ear canals, and I've always struggled with fit; the Apple ones are the worst.

I have the Sony earbuds, and while I agree they fit a little better, I find the memory foam disgusting. It also degrades over time and becomes brittle. My solution was the Alza SednaEarfit Max, which are silicone earbud tips that fit the Sony. They are easy to clean and come with the tiny mesh that prevents ear wax from getting into the electronic part of the earbud. Of all the tips I've tried, these stay the best.

However, they still fall out too easily if I'm eating (from jaw movements) or lying on my side.

PS. You mean Sony WH1000MX4. Not Sennheiser. Although Sennheiser makes the Momentum True Wireless, which comes with silicone earbud tips.