Finding Relevant Decision Makers for Target Companies

Hello, do you have suggestions how to find more relevant decision makers for target companies? I'm trying to find all the sales directors and legal counsels of the target companies. I have a list of +500 companies but I can only find around 100-150 target decision makers. I've noticed that I can find more relevant decision makers when using Sales Navigator. I've tried to use experience section and also the job title "seniority" and "job functions" and "job titles". Only using experience is tempting as I can find already 250 decision makers, but then I'm having all kind of marketing directors and CEOs in the list. Then I would need to find out somehow if they're relevant in sales or legal field. Any tips? 😅