Attaching an altimeter to the ProXR Lite A to D inputs

I am working on a project to use an eight channel ProXR Lite relay board to enable elevator floor buttons on an eight floor elevator.I only want the floors “turned on” if the elevator is at the ground floor.
I want to use an altimeter to sense when the elevator is at the bottom floor.
My problem is that I can’t find a suitable analog sensor to use. They all seem to be I2C or SPI which I don’t think would work with the relay board.
Does anyone have a suggestion as to what sensor I could use?

I’m not sure what I would recommend for that.

Are you controlling the ProXR Relay controller from custom developed software running on a computer?

I don’t think an altimeter would be the best option for determining when the elevator is at the bottom floor. I would think something like a proximity sensor would be better. Something like this perhaps which generates a dry contact closure which could be connected to the ProXR A/D inputs:

Yes, I am controlling the relays with a windows service. The service receives an access control code and converts it into a floor. An HTTP request is sent via WIFI to the relay controller that is on top of the cab. The relays enable a floor button.
I am trying to avoid any sensors placed in the elevator shaft. Elevator companies are very anal about doing that.
I found an Adafruit BMP280 I2C or SPI Barometric Pressure and Altitude Sensor and a Adafruit MCP4725 Breakout Board - 12-Bit DAC w/I2C Interface. I don’t know if they can stand alone or if they need a microprocessor to drive the I2C.
I am experienced with PCs. The microprocessor stuff is a mystery. Your advice is much appreciated.