Add-on [Paying][XF 1.5] Add option "Search this forum and child forums" to quick search

[sub_ubi]

When browsing a forum, I'd like users to be able to search that forum as well as its sub-forums from the quick-search bar. Example:

Here's what quick search looks like by default:

In addition to (or instead of) "Search this forum only" I'd like "Search this forum & child forums as well"

I pay well and on time, you can ask other devs here. Thank you for any advice or estimates, or links to add-ons that already do this.