12 button controllers are how leverless controllers started—since you have four buttons for directional inputs and eight buttons for attack inputs.
The SYGBox by SaveYourGames is a 3D printed controller that lets you choose button and cable colors as well as the PCB.
Retro Stockpile offers enclosures in the leverless & fightstick formats that can also come preassembled with buttons and other parts.
The Mavercade Heavyweight is the Francis Ngannou of fightsticks—as it allows you to throw punches with some weight!
This fully customizable controller is also available in arcade stick format for those based in France or willing to ship from France.
The OkiBoard is a leverless controller that adds to the arsenal of controllers coming from the United Kingdom.
The Jabslab Digital Combat Controller is a mini LED controller with customizable artwork and other included goodies.
The X8 is PXN's debut WASD-style controller that sports some interesting artwork which is refreshing to see.
3D printers can make the mini Flatbox controller at home or simply order it preassembled for maximal convenience.