I’m not a huge fan of commercial brackets, even though I am currently using a standard house style futon sofa/bed, but I also usually sleep on it in sofa mode, so the mech actually gets very little use.
I’ve built a lot of them though for myself or helping others, and never used store bought brackets. My typical criteria is simple, reliable, durable, foolproof, and comfortable. The first two pictures below were hands down the most comfortable, due to the angle of the seats, but it was also the most complicated to build.
The middle picture is a simpler box design, but gives the same level of comfort. Instead of pivoting legs, it uses rails on the side walls of the box it sits upon. Besides the seats lifting up, I also added sliding doors front and back for easy access to the storage underneath.
The bottom picture is a typical double sided boat seat. They can easily be built as wide as you wish. They sit on a box, and except for the front legs, the box supports them in both seating and bed mode. The seat is usually flat with that design. It’s a very simple, straight forward design, just not as comfortable.
If none of these tickle your fancy, let me know… I have built many other types as well.
"If you prepare for the worst, every thing else is easier." ~ Off Grid