Custom URL structure for posts, etc?

I have a software website. I want these URL types:

example.com/download/post-title/

example.com/tag/keyword/

example.com/category/keyword/

As you can see, everything should be normal WordPress URL structure except the posts, which should have a URL base called “download”…

The problem is that I can’t simply put all the posts in a category named “download” because I need to use the category function for organizational purposes.

I also can’t use a custom structure like “/download/%postname%/” because then all the URLs will get weird, like when I want to post an actual “blog” type of post on the site that is not a “download”…

Anyone got any hacking suggestions?? Cheers!