Is it possible to get a mock up of veneers without committing to the whole procedure?

Yes, you can have your dentist  draw up a realistic digital simulation during your initial consultation to show and visualize what your new smile can look like with veneers.  Expect to pay anywhere from $195 - $500 for this visual service though some cosmetic dentists include this for free with their consultations.

This is are not fillings and planning is the key to success.  It sounds like you will be an additive case which makes mock-up far more predictable.You might also want to consider Epigenetic Orthodontics/ orthopedics with DNA Appliance to 3 dimensionally grow your maxilla supplying bony and tooth support for the soft tissues of your face and has positive physiological effects as well.These can also ber combined often with better results than either one alone.

You can absolutely have a veneer mock-up to preview how they might look and feel.  You need to find a dentist proficient in cosmetics who can provide this service.  The fee can vary and can, at times, be part of the overall veneer fee.