Even low gravity will keep your atmosphere close to the surface. What causes atmospheric erosion is solar wind, and the reason Earth isn't affected (much) is that we still have a powerful magnetosphere, powered by our spinning molten iron core.

Mars has a magnetosphere but it's much weaker since its core is cooler and slower and smaller.

If we nuked the polar ice caps (or similar method to warm + evaporate them) it would generate enough of an atmosphere for the external pressure to be livable - maybe even breathable.

Since the magnetosphere is still weak, this atmosphere would be eroded over time, but we're talking tens of thousands of years or more.