These photos show the interior of a simple dining chair. Imagine how much more complex the inside of an armchair or sofa! 

Traditional upholstery requires many different techniques in order to give the furniture its characteristic shape and comfort, so sticking in some foam  or doing a little DIY project is a really bad idea, you will ruin the shape and value of the  furniture. 

This small chair alone required webbing, springs tieing carefully on, a layer of hessian, a layer of coir or hair stuffing, another later of fabric onto which stitching produces the specific shape of the chair, another layer of soft horse hair for comfort, a layer of calico to enclose all the stuffing and finally the top fabric. It can take a professional dozens of hours to do just one chair depending on it's complexity. 

When you ask upholsterers to give you an estimate to reupholster a chair, find out what they specifically intend to do or what they feel is necessary. Sometimes some things can be repaired but your loved item may need to be fully upholstered. If you get a very low quote, chances are they are not doing traditional upholstery and after a few months, you will be very disappointed with the look of your furniture.