You've actually stumbled into something pretty similar to the philosophy of Polynesian navigators!
Part of their approach to navigating the pacific ocean was to envision themselves at a center of a circle, with the islands, stars, and ocean rotating around them. This would help them maintain a course in the general direction of where they were heading. Then, when they reached certain points in a journey, they'd switch to more active forms of navigation. These methods meant that they very reliable could both find new land, and adjust their course as they zero'd in on their destination.
It's also important to mention that this perspective is extremely difficult to translate to a map. Which for the Polynesians, wasn't that big of a deal! Instead this knowledge was passed through oral tradition, which was far more useful for this approach to navigating the world, especially because their routes and methods would change depending on time. Because of this, when attempts to translate this knowledge into maps happened, the results were illegible to the western perspective.
What does this mean for you?
Like the Polynesians, navigation would probably be done by expert navigators, rather than having a series of tools that allow anyone to navigate. For the first part of a journey, the navigators would consider wind currents for the time of year, allowing them to generally get a sense of where an island will be. Then they'd head in that general direction, probably using a star compass to maintain their bearing. Additionally, the shifts in elevations may affect the movement of stars. A skilled navigator might note how certain stars are eclipsed by the presence of land.
Once in the general area of a land mass (several 100 kilometres), they'd switch to more active methods.
Clouds tend to form more heavily over the ocean (https://atmos.uw.edu/~rmeast/OceanCloudsweb.pdf) and sit at a lower elevation than above land.
While your world doesn't have an ocean, the shifting elevation of the drifting islands would certainly help. Navigators would keep an eye out for gaps in cloud formations (indicating a landmass beyond the horizon), as well as looking for cloud formations that are more likely to appear above land (I'm not sure how your atmosphere would affect this, but there would still be some differences due to the temperature shifts between land and open air). Additionally they might look for cloud formations at incorrect elevations, which would indicate an island being slightly lower or higher than they expected.
Wind and air currents
The presence of an island would also be noticeable through the way it impacts air flow around it. Polynesian navigators were able to locate an island based on how its presence would disrupt the wind nearby. An easier way to imagine this process would be like a rock in a river. Even if the rock wasn't visible to you, you could still see the wake and ripples that occur as the water moves past it. Your navigators might look for pockets of dead air, indicating that they're in the 'wake' of a ladnmass. Or, from further away, they'd learn to recognise the turbulence caused by the presence of a landmass. There's some photos on this page that might help to visualise this (https://en.wikipedia.org/wiki/Wake_(physics))
Fauna, and other close indicators
As they drew even closer, navigators would then look for signs of animals that indicate a landmass. In the morning, they'd look for birds leaving their homes to forage and head in the opposite direction. While in the evening, they'd follow the direction of birds as they returned to their nests.
However, since there's very little reason for birds to venture out in your world, this method would be slightly adjusted. Instead, navigators would try to align their voyages with the migrations of birds. The idea being that they try to estimate the final leg of their journey to coincide with birds returning to their home islands.
Additionally, there are several minor indicators that could be used to more finely search out a land mass. Polynesian navigators noted that when they were close to an island, they would be able to smell the difference in the air (compared to the smell of the open ocean).
Navigators in your world might be able to tell the difference in light that indicates that an area is in the shade of an island. As well as the shifts in temperature and humidity that indicate a landmass.
Hopefully these methods are helpful, I know this post is a little old but I couldn't help myself from sharing some info on Polynesian navigators!