Hi {{first_name}},
Thank you for taking the time to talk today. The conversation was more useful than I expected, especially your point about [[specific insight or advice they gave]].
Here's what I'm going to do with it: [[1-2 sentences on the specific action you'll take based on their advice]]. I'll follow up once I have results to share.
If you're open to staying in touch, I'd welcome the chance to check in as things develop. If not, I'm grateful for today's conversation.
[[Your name]]