For a small annual fee, you get 1 TB of OneDrive storage and the latest Office apps. The installer is lightweight and always up-to-date. If storage is your concern, this is the best official path.
If you want to avoid the risks of third-party websites entirely but still need an efficient way to install Office 2019, you can use Microsoft's official deployment methods designed for IT administrators. The Office Deployment Tool (ODT) Download Microsoft Office 2019 Highly Compressed
A fully licensed, malware-free installer of about 1.1–1.4 GB. For a small annual fee, you get 1