Hey Sunny S. just because you mentioned scalability and third-party integrations, I would recommend HubSpot. They've been in the space much much longer than Attio, so you'll be able to find a lot of resources to help you build out the system and processes.
I've tried out Attio, it's a good tool for small businesses, but so are Pipedrive, Zoho, and Monday.com. When it comes to scale, HubSpot will be a better option.
