The 8BitDo Micro Controller is a Bluetooth gamepad with a 16 different inputs that you could fit into your back pocket. It costs $24.99.
Wireless controller 8BitDo Ultimate C 2.4G
Play any game, anywhere. Nintendo Switch and Windows PC. 8BitDo controllers are designed to be as versatile as possible with each of your modern devices. Now with a 2-way mode switch, you can instantly pair your controller via Bluetooth.
8Bitdo Ultimate Bluetooth Controller with Charging Dock(White)
8BitDo Micro Review - Tiny Switch Controller!
The Best Nintendo Switch Controllers in 2024
8BitDo Micro Bluetooth Gamepad
8BitDo Micro Bluetooth Wireless Gamepad for Nintend Switch Windows Android macOS iOS iPadOS Raspberry Pi Game Controller
8BitDo Lite - 8BitDo Lite
Weighs 24.8 grams featuring 16 buttons. Ultra-portable and versatile., Compatible with Switch and Android, Supports firmware update, Mode switching
8BitDo Micro
8BitDo Micro controller: where to buy the Switch and Android controller - Polygon
For anyone wondering about the 8BitDo micro : r/SBCGaming