Create an administrator-like profile/role outside the management account

I have multiple accounts in Organizations and wanted a way to manage them securely. I want to create a user or give my user permission as if they were an administrator (in this multiple accounts), so I don't have to use the management account. What's the best way to do this?

I saw that I can use permission boundaries, but I didn't find examples of how it would be applied to an administrator-like user or how I can write a policy and permission boundaries in this case for an administrator. Besides that, would any other action be recommended? Any blockage on the management account? Thanks!