I'm thinking that the height of the file cabinets may not be right---you really do not want to scrunch down or up for long periods of time!!!
How about an old dining room table?? If it is too tall...have DH cut the legs to the right (for you & your machine). That would give you length and depth!
I do not have a lot of room so I went with a sofa table--length to the side and a decent depth!! And I cut the legs to fit me!! And cut some plywood for an extension table for the sewing machine---works great!!!