I have found pads that are on these headphones to work really well:
https://www.amazon.com/LyxPro-OEH-10-Headphones-Comfortable-Interchangeable/dp/B01G90XT3O
The Lyxpro OEH-10 headphones.
Just make sure to keep the filler material from your m40x's behind the pads. That helps keep the sound signature sounding good.
You can buy those headphones on that company's main sight for around 40 something dollars and cheaper than amazong.
That would bring you to around the same price as those zmf style pads, plus you get a free set of headphones lol The headphones aren't great though, have some simblance, but they are useable for things like gaming.
The pads aren't as thick as zmf or others of similar style, but they make the sound signature have a tad more bass and gave my m40x a fuller sound.The pads on those ecompass the whole ear and are very comfortable. Those headphones come with velour pads also but they did not sound good on the m40x as the sound escapes. Only the pleather/vinyl looking ones worked really well.
When I switched my stocks out with these pads from this headphone, I was amazed at the sound signature. It was perfect. Still very crisp with a bit more low end but not overpowering. It put the sound in a really nice place, almost perfect, but certainly better than stock in my opinion.
I'm also about to try out these :
https://www.amazon.com/gp/product/B07M7MMNCR/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
They look very promising as they look similar to the lyxpro pads in thickness and design. They have good reviews for sound signature. I'm betting these ones will be the keepers and my recommendation, but I'll update later. For now I'm very happy with the pads from those lyxpro-10 oeh.
Otherwise, yea, some people say the ZMF SHEEPSKIN angled pads are the way to go and maintain sound signature with a bit wider soundstage, but I just don't trust them as I've had a bad experience with some similar pads that were supposed to sound great too.