Welcome
Can't help re armrest, although I am sure its do-able- best source one from dismantlers
Re mirrors- you will need;
folding mirrors
folding mirror capable door modules(control units)
new window/mirror switch for drivers door
-To do this through a dealer will be a joke(silly money) & they may even tell you its not doable. To do with new parts yourself will probably cost best part of £1K! Even with second hand/ebay parts will be v expensive & you will probably need to keep an eye out for some time to get all the parts you need.... (unless you find a car at a scrappies with everything on it you need)
If you don't have one already, a simple, quick & most satisfying upgrade is to fit a dimming rear view mirror which is simply 'plug & play'.
BTW, a lot of parts on the W169, including (afaik) the mirrors, are also used on the W245(B class), so you can also search ebay for B class parts to fit onto A class.
Silver or blue(Osram diadem) indicator bulbs also look better on the front imho to get rid of the 'egg yolk' look.
Try to get some pics of your car on if you can