This is about the placement of a search option on a products listing on a smartphone.
Between 4 scenarios, which is the best according to you? :
Search button at the top of the scrollable content (disappears on scroll down).
Search button at the very bottom of the scrollable content (appears only when all products viewed + doesn't work with a lazy loader).
Search button placed in a "actions" dropdown menu located in a vertically fixed header.
Search button (with icon) placed directly in a vertically fixed header.
I would choose #4 because my experience plus gut feeling tell me that the search button should always be clearly visible on a products listing interface.
This allows to quickly perform a search from any scroll position which I find important on a mobile UI (no need to scroll back at the very top).
The problem is that I can't find any resource/reference to back up my choice.