Check out DeskPins. It should do what you are looking for.
DeskPins allows you to keep any window on top of others with a few clicks. While many programs offer this as a feature, others do not, and in such cases DeskPins comes handy. In addition, you can also define rules that use the window title (with wildcard support) and can automatically keep any window on top that matches your rules. The `on top` window is marked with a colored pin that can be quickly removed by simply clicking on it, returning the window to its normal state.
You mentioned a need for global hotkey feature. If the "pin" is not enough, try Always on Top Maker.