I was in a similar boat to you (no pun intended!) @Lebesgue a few years ago. I needed a boat with the ability to sleep 4, 2 in a double and 2 in singles.
While this layout is very possible, it's surprising how rare it is. Lots and lots of boats have a double at the back and a saloon at the front with two captains chairs. Longer examples might add a pullman dinette that can be converted into a double, providing 4 births in total but not single births as required.
As mentioned, Ex hire boats often have a suitable layout but their fitout can be a little basic and might not be to your taste. However they do come up 3rd hand where the previous private owner has carried out improvements, which is worth looking out for.
I did find a suitable boat eventually but it took a year!