We have a prospecting master class coming out this fall, it takes students through the 13 Prospecting Strategies to test and master to they never have to worry about where the next client is coming from...but that's too far for you to wait, so..
Since this is a B2B sale, who is the person at the company that cares most about this problem? Who is most affected by it? That is person you want to target (a simple introductory email after a LinkedIn invitation works well). What is the value prop? Is it saving money? Being environmentally conscious? Meeting certain regulations? Depending on what you're selling and how you're selling it, it will lead you to different departments.
Specific to your product, there are consulting agencies that exclusively help companies with their social and environmental impact, so they would be great partners for you. Google is your friend for any of this kind of research!
As far as a CRM, we use Solve360. It's very affordable for you as a solopreneur and is easily customized without a developer. Your crm basically needs to keep track of your contacts and conversations, remind you to follow up, hold documents or links to relevant documents, and generate reports of data that is important to you (emails: responses: discovery call: appointment: etc) so you can plan for the future.
Going from marketing to sales are different skill sets, so I would highly recommend getting some formal sales training under your belt, as I'm sure you had some marketing and advertising training in the past.
Good luck on your new venture!