I have multiple accounts and manage various for some clients too.
I use lastpass and more and more Firefox because of there "Multi-Account-Containers" add on to avoid such issues.
https://www.techrepublic.com/article/how-to-use-the-firefox-multi-account-containers-extension/
https://lifehacker.com/here-s-why-you-should-embrace-multi-account-web-browsin-1816209401
Profiles allow you to have different overall settings, extension, etc for the same browser. Cookies are open and visible to all tabs. For example, if you want to log into you business gmail account & your personal gmail account: 1) you will have to log out of one account to log into the other 2) open a new incognito/private window 3) Open a different web browser.
Containers deals with cookies. Only tabs created in the same container will share/see each-others cookies. This mean that under the same session, you can have your regular session, & multiple containers (work, research, banking, you name it) keeping each separate. For example, you can log into 2 different twitter accounts (one under each container) keep each & their opened links etc too their respective container.
*Perhaps A better explanation is found at the extension's page.