How to best control my 2 speed fan.....here we go

Just installed my a/c, I have a 2 speed electric fan (don’t need to know mechanical fan is better. I have no room for it) I have what I Have.
Right now I just have The low speed running off a fan relay with the thermostat in the radiator. I have used this for several years with no issue.
Now I have A/C and need to run the fan with that. What is best way to to this. I don’t have a trinairy switch just a low pressure, but can get it. Do I need a controller like Dakota Digital. What are my options.