You ask two questions:

1. How to find the "decision maker"
You make a potentially dangerous assumption here. Understand that there may be many "decision makers". Most of them can say no and nix the deal, but (usually) only one of them can say "yes" and the sale will happen.

Is your sale simple or complex? If simple, i.e. there is only one person involved in the buying process, then all the answers here are correct. If your sale is complex, i.e. there are many people involved in the buying process then you have a very tricky problem as each of them may have a different perspective on the business problem, the way to address it and how important it is.

2. Ideal Customer profile
What you describe, "companies based on revenue, geography, etc" is the target market, it is not the ICP. The ICP talks more about the issues and problems that you solve. So, an ICP within a target market would include factors like:

- Companies who are growing rapidly and who struggle with communications among remote employees
- Companies who require up-to-date information to employees while out of the office
- Companies who face tremendous pressure to grow despite a down market

About me:
I deal only in the world of complex sales. If you want to talk about selling this this world, then contact me. If you are in the simple world (not that that is a bad thing) then one of the other experts will be able to help you much more.