Many times it is cheaper to go to the local home improvement store because of the cost to ship 1 cable. You could use these ads as examples of what you need to look for.
Monoprice is known good brand but costs a bit more. They clearly tell you the type and size of the wire. They make it a point to indicate that the cable is eia/tia compliant.
https://www.amazon.co.uk/Monoprice-ZerobootCat6-Ethernet-Patch-Cable/dp/B00Y42E34O
This was hard prices vary a lot because of color ?
You will have to dig around to see if they have other options.
The first is a stranded cable which is more flexible but it does not have as nice ends on it as the second cable. Note if you ever crimp ends on the cables you need different plugs for stranded and solid cables.
As a note monoprice lately also sells trash cables. They clearly state the wire size is 31awg and unlike some other vendors they do not pretend it is compliant with the standards for Ethernet cable.