If we changed our tactics to not play poverty tiki taka around the back 3, and hopefully play a back 2 then this problem will be much less significant
As for unreliable defenders, get used to it.
Pretty much all the top teams have an unreliable, mistake prone CB in their starting XIs. You juve have to defend as a team. Unless we throw PSG money about there's no way in hell we get a near perfect pairing of CBs.
If we could actually attack with directness and intent against top teams, we'd be worrying less about absolutely needing a clean sheet in order to get a result. Our defence is fine on the whole, improving our defence or our CMs at this point would cost a lot and give us a little.