The formatting items you've mentioned and easily be accomplished by clicking on the PREVIEW POST/REPLY button after your entered your BBCode formatting.
A WYSIWYG editor for UBB.threads is something that I had started work on a while ago. It currently has a few major bugs in how it treats HTML/BBCode, and cannot be included as part of the UBBT package until those bugs are ironed out. But it is in the works. It is a low priority on the "things that need to be done" list, but it is on the list.
A screenshot of that work:
If your discussion forum requirements have changed from using bulletin board software for sharing communication, and you now desire an entire document suite to get ideas across, why not embed Google Docs/Sheets/Slides, Adobe PDF attachments or Microsoft's "Word/Excel/PowerPoint for Web" sharing? The tools have been out there for a few years already, and they are free.
To embed a document from Google Docs/Sheets/Slides, from within your Google Drive, open the document you want to embed and click on the "Publish to the Web" link under the "File menu." Then "Embed" and copy the code into your post as "HTML only" or "HTML and UBBCode" from the Post Options section. But since allowing random/untrusted web users to post with HTML is a security risk, choose the "Link" option and add that in to your post with UBBCode as a URL.