Its harder to find a top-class left-footed CB, or am I wrong? Still prefer Laporte.
Or you can try to pick a CB that can use both feet. TS and DL can use both their feet. Marquinhos can do it too and trains a lot with both feet during training at the Ooredoo center. All three can do passes, long passes and shots with both feet. Hell, DL scored with his left foot last night.
All three can play on the right or left CB position.
I don't say that choosing a naturally left-footed CB could not be better, but it should not be a reason to discard other choices when there are ambidextrous players around.
I being a PSG fan aside, as a barcelona follower, if I had to pick between an ambidextrous TS or Mathieu, I would pick the former.
My point is that if Barcelona still plans to pick marquinhos in the future, then he can play CB on the Left and it will cause absolutely no problem.