A family of Microsoft word processing software products for creating web, email, and print documents.
Microsoft 365 provides a cloud backup that meets most people's needs. As long as you have an alternative backup strategy, you can certainly do without Microsoft 365.
If your husband has purchased a Microsoft 365 Family plan, you can get on his plan for free. In that case, purchasing a separate plan would add no additional benefit to you.
See plans #2 and #3 here. Both are family plans: https://www.microsoft.com/en-us/microsoft-365/buy/compare-all-microsoft-365-products