Debian or Xfce or Tails are the options that will work for you on that old computer and it is better to use Tails.

 - Delete everything on the memory, delete Windows and make sure to format everything.
 -  Remove all the connecting parts from the network cable to the Bluetooth.
 - burn Tails on your computer and use electrum to generate the addresses and MPK.
 - Save the wallet seed on a piece of paper or a metal piece.
 - import the MPK to the wallet on your phone.

You can find more information here or by searching on Google for tails electrum cold storage

https://electrum.readthedocs.io/en/latest/tails.html
https://www.youtube.com/watch?v=1e6IDTP3g5o