Could use hydraulic (oil) bearings instead, that would be plenty stiff and air bearings are mostly useful for high surface speeds and/or to avoid transmission of vibration which are two features that won't really be an issue for you. In the same vein you could use a magnetic bearing, stiffness is higher than an air bearing and also a programmable feature, but the most involved type in terms of design.
Allowable size tolerances on the oil bearing would be looser to.
Still, given your application it would seem a bushing would suffice and a rolling bearing would excel. In our robots that we build at work we are using a lot of cheap plastic bearings actually, but we have a complex pick and place situation of light objects, 99% of the bearing load is just the robot dynamics and not the material being moved. Plus we design iterate and rebuild all of the robots every year since we don't sell the equipment to the clients and we're still in startup mode.
Our investors, which includes two major SCARA and industrial robotics suppliers, favor large rolling element bearings. They withstand the abuse of customers very well and for some reason no engineers ever want to admit they crashed the $65k 6-axis robot into something when they were dicking around...