If we are set on having AWB as our starting right sided fullback for the foreseeable future (a mistake in my eyes), we need a left sided fullback that is excellent on the ball and can cross with some accuracy from deep. Being able to contribute effectively in the build up and progression of the ball into the final third and offer a threat from wide... So that we are not being stopped by teams putting 10 men in the middle of the pitch and thus limiting the space and time on the ball for our midfielders...
A left back with the abilities that would make it look like he could function well as a midfielder is what we should look for.
From the EPL there are two standout alternatives: McNeil (Not currently a leftback) and Chilwell.
Guerrero at BVB, Telles and Grimaldo are other alternatives that on paper at least look like good options.
IMO Shaw and Williams are far from good enough on the ball to make up for AWB limitations when the team is in possession. Shaw is decent and not an obvious weak point besides when it comes to crossing and injuries and taking time to get fully fit, but does not really offer anything other than being a Zero-sum player. Williams is a future second option at best and with his aggressive mentality the ideal squad player (Like McT). So if we have the funds to get a more suitable left back we should, because none of our alternatives is good enough long term and playing Shaw/Williams/AWB will hinder our build-up/progressing of the ball next season.
The only fullback at our club that seems to have the abilities to function as a modern attacking fullback is Laird. And I can see the arguments of giving AWB 1-2 seasons to improve his attacking play and on the ball capabilities (Would require a total rework of his way of controlling the ball and is unlikely to be successful...) while waiting to see if Laird can stay fit and adapt to the EPL.