Jon Wild
Only mass of material stops sound, the denser the material, the more sound will be stopped. A very heavy wooden door will do the job triple glazed or double glazed will work but insist og 6mm or able glass. solid 10 to 20 mm glass would also work. The fit must be perfect so you may want to consider a new frame as well. All the seals must be perfect The more mass you install the better it will be - explain to the joinery shop that sound is your main criteria. UPVC door and frame, will be a waste of time and money. There are some very good composite doors but oak or Sepelie take a bit of beating for density
