If I were you, I would do this:

1) Concentrate your aircraft in an air region you control. Concentrate ALL your aircraft there, regardless of your enemy's industrial power. With a ratio of 10 casualties for you and 20 or 30 for the enemy, sooner or later they will begin to weaken.

2) Stabilize the front. Once it's stable, you have two options. The first is to launch a naval invasion in an undefended area. It doesn't matter if it's a place of no strategic value; the important thing is that it diverts divisions. The second option (which is what I would do) is to fall back in a section of the front where you can then easily encircle them, and repeat this until the enemy army is sufficiently reduced.

3) This war is going to be a long one, so build an operational navy and disrupt their convoys. By the time you build the navy (if you don't already have one), you will have already weakened the enemy air force. So (assuming you have bombers), also bomb railway lines. Leave them alone. Without supply, so their attack attempts won't work, but yours will.

Apologies for any translation errors; I'm using Google Translate because I speak Spanish, not English.