This article describes how to set up a bluetooth mouse with Archlinux. I used a Logitech v270 with a Trendnet TBW-101UB USB Bluetooth dongle, but the general process should be the same for any model.
You need the bluez-utils and bluez-libs packages from the community repository.
The pertinent options in /etc/conf.d/bluetooth are
after that, start bluetooth services with
Finding out your mouse's bdaddr
It is of the form 12:34:56:78:9A:BC. Either find it in the documentation of your mouse, on the mouse itself or with the hcitool scan command.
# modprobe -v hci_usb bluetooth hidp l2cap
loads the kernel modules you need, if they weren't loaded automatically.
Connecting the mouse
hidd --search hcitool inq
are good for device scanning.
hidd --connect <bdaddr>
to actually connect.
will show your currently connected devices. The mouse should show up in this list. If it doesn't, press the reset button to make it discoverable.