doc doesn't have a great way to get re-grounded, but he does have mix up options (assuming he isn't being combo'd)
D.air works well to outprioritize oncoming attacks from below, n.air works better when you're more likely to trade. You can always stall with cape to mix up your fallspeed/timing.
Airdodgeing is scary, but sometimes its your best bet too move past an anti-air attack--even if you get punished for it, its often worth it, just to improve position.
and I will forever preach this- Tornado has its use here. If you can bait the opponent to whiff an uptilt/etc, and mash B (only slightly) to temporarily hover right outside their range, you can sink with the ending hitboxes of 'nado to punish and make it back safe.
If you're offstage, pills are good but they'll get you in trouble vs most good characters b.airs off the edge, so you gotta be ready to pill and airdodge as they try to intercept.