After searching the smallest VHF/UHF transceiver with still enough power I found one that looks great and has the right specifications.

It’s a dual band (2m / 70cm band) transceiver, 25 watt maximum power and VERY small.

The model is the QYT KT-8900 from China.

I made a video that shows the unboxing of this little gem.

Some links where you can find these transmitters:
Aliexpress Link 1
Aliexpress Link 2
Aliexpress Link 3

Or just Google the type name of the transmitter and you will find one! 😉

Programming software for this little rig you can find here.