Here’s a couple of cheaper ideas you can try before replacing your unit:
I have a smart thermostat that lets me configure the fan to be on X minutes every hour. Helps circulation, evens out temps
it has remote sensors, and I can tell it which to follow at any time or to average
I have partly closeable vents, so I can direct more heat downstairs in winter, more cool upstairs in summer. This is not as effective as dampers and you need to watch shutting down too much airflow, but it’s cheap diy that can make a difference
my brother swears by pointing a pedestal fan up the stairway