Props for taking Slack as a starting point for selecting new software. Personally I like having relevant slack notifications in corresponding channels (Eg #sales, #research etc).
Notion – a heavily underrated team collaboration tool – allows you to set up different activity in 'pages' to different slack channels with fine grained control.
Notion is not per se a project management tool, but rather a very smart and flexible documenting and collaboration tool. We use it to manage projects for high profile customers, log meetings, write out new product ideas, document our software and more. Where slack is our dynamic team home, Notion is for static information.