Just level in DPS offspec. If you really want to “main” your resto, just keep all AP upgrades and use them on resto artifact (available after 102). The amount of AP gained through leveling looks not really significant compared to 110 lvl activities to me mostly because the cost of traits increase exponential. 14th trait costs as much as first 13 total, as example.
Also as i read in article at healiocentric leveling as resto is not much slower then leveling as ele mostly because you spend much less time restoring between pulls.