So you want a starting standard centre-half AS WELL as a starting standard central midfielder and a backup to Lukaku? Did we win £40m for beating Southampton? I don't know if you've been away somewhere remote, but we're Everton and we don't have much cash.
Jags is out for maybe a month. After that, Alcaraz and Stones are two decent backups. Conversely if either Barry or McCarthy are out (and given their proclivity for collecting yellow cards, it will happen again soon) then Osman is in the starting lineup, and that's far more worrying than Stones getting game time.
We need a CM far more than a CB, so we should pick up the CM now and wait until summer for the CB.