Yes, Mahrez has been superb, and would normally be my choice, but I have gone for the more athletic, hence Walker over Lewis, just to combat their pace on the wings. We give away a little ball control by doing that, potentially, but it should be more defensively solid. Gundo for Bernardo would be the other option.
I think Ake is a shoe in on the left, because of the way he dealt with Saka in the cup game. If he plays, there is always an argument for Lewis because of the control he brings to the midfield, but Lewis against Martinelli is, naturally, a higher risk. If we go more risk averse at the back, I think we have to be more creative further forward.