Koscielney - He's a little tto lightweight to play alongside Vermaelen in the middle, he's great on the ball though I think he would be excellent at LB.
And may i ask where you proof of this is?? Because at Ajax he played as a CB alongside Johnny Heitinga and when Heitinga left and joined Atlético Madrid in 2008 TV then played at CB with Jan Vertonghen for the next season before joining arsenal... Do some research mate...
Oleguer and Vertonghen played most of Vermaelens last season as the CBs, with TV at left back. Toby Alderweireld and Gregory van der Wiel also played at CB in games wherein TV was at LB.
I think in a top league, your left back should be a left back and not a centre half, who can fill in unless it is an emergency.
Baines is the best option although i dont see Moyes letting him go for anything under £10 million, so the cheaper option is Jose Enrique and Gibbs is nowhere near good enough, yet