A few things to prepare a good start

Your device will work without a Q-Strip attached. First program and connect Your Arduino nano IoT with the Arduino Cloud. If that is done, You can place the Q-Strip on top of Your matress as being shown in the pictures. Chest height. If possible make sure You fix Your device to the side of Your matress. For now we use double sided tape to have at least some fixation.

The sensor is attached to A0 analog input of the Arduino nano 33 IoT. You will not need any libraries.

Whenever You want to sleep, just go bed normally as You always supposed to do.