Look at this stuff
The CO2 line is resistant to CO2 and will not degrade, brittle and crack as typical hose from the hardware store will. 5/16 ID is typical.
The beer line here is 3/16 ID and will not give the off flavors which have been mentioned.
Both hoses are rather thick walled to help prevent kinks in the lines.
There are many places to get this hose. The link above is just one example.
For the price, why use anything else unless you need it today