It's always better to find the leak. You can use a spray bottle with soapy water and spray around the lip and valve stem. The other way is to remove the wheel and submerge it in water to find the leak. A tire shop can find the leak and is the best choice. A tube can work but in the end, the expense of the tube, dismounting and installation, etc. is a bandaid. Take it to a tire shop, please. Stop loosing sleep and inventing extra work and expense over it.

Les