Hey! I was in the same situation a few months ago. Manually migrating Thunderbird emails is honestly a nightmare. I tried a few methods before landing on Softaken Thunderbird to PST Converter -- and it worked really well.

It converted my Thunderbird MBOX files to PST without any data loss, kept folder structure intact, and the whole process was surprisingly quick. No technical skills needed either -- pretty straightforward interface.

Just install, load your Thunderbird profile, and export. Worked perfectly for me. Give it a shot!