Just a minor frustration, I have not found how to do this, double clicking serves what purpose? Am I going to change my mind between clicks?
Did you try going to the PCMANFM file manager, and with it open/running go to Edit > Preferences > Behaviour and select “Open Files with single click”.
I have not tried that setting myself to see if it works, nor to see if it requires an LXDE restart to function after setting, but you could give it a try and let us know how it works.
Thanks @oldcpu, yes, and no restart of LXDE needed. I was looking in the wrong places for that option, thanks again.