We don't recommend to do this even in header search. It's because search layouts for products and posts are totally different as well as all functions. You will have many incompatibilities if you have both in search.  

At the moment using the search form provided in the Visual Editor it only has the option to search Products or Posts (one or the other and not both). However we would like a search form that can search products and posts simultaneously like the search form that is in the header above the menu. Is this possible?

https://www.myservices.vu/

Thank you

Jordan