From my experience, SDL does not play nice with widgetry libs because they both want to assume control over the overall program. SDL doesn't even particularly play nice with multiple windows.
This is one of the many reasons I don't really like SDL anymore.
The easiest way to do this with SDL is probably just to use SDL exclusively (do not try to use any other widgetry libs) and use one of the SDL add-on libs which add pushbuttons and other common widgets to your program.
However that sticks you with some limitations.
1) You can only have 1 window
2) Your controls won't look/behave quite like normal controls would.
Personally... I prefer to use SFML. Not only is it just overall a better library (IMO), but it also plays very nice with widgetry libs. In fact there are 'drop-in' classes to create an embeddable canvas for both wxWidgets and Qt (two very popular, crossplatform widgetry libs).
I have had great success in this very recently (like 2 days ago) by using this page as a guide:
It's very possible that there might be something similar that works with SDL... but I'm not aware of any.