Chris, I would recommend a Gloria sprayer as they really are lifetime sprayers and parts are readily available, go for a stainless steel one,
You can integrate a QD's for swapping between fabric spray gun for upholstery and lance for carpets, will take some messing about getting correct threads though.
Don't get a plastic sprayer, they don't pump up high enough for the PSI required for protector applying. You want high PSI for a better spray pattern. (around 50 psi)
My preference on jets is 65/01 upholstery gun
80/02 on the lance for carpets,
Craig.