for the BOSE system you will need the standard factory head unit. you will then need the wiring harness that runs from the head unit to the BOSE amp. not sure exactly where this fits on the 147 but on the 156 it was in the rear parcel shelf.
from the bose amp you will then need the wiring from the amp to the speakers. the BOSE speakers run at 2ohm impeadance I think rather than the 4ohms that normal speakers run, so you will need the speakers as well.
honestly the BOSE system is a good sound system, however its not a practicle upgrade from a base factory unit.
you will be far better off in the long run buying a good aftermarket head unit which has a high power output then upgrading the door speakers to something with a nice heavy magnet and solid cone, preferable something component.
if you make sure you get something that also has some pre-outs at a nice voltage level you can put some speakers in the parcel shelf and a nice sub in the boot.
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso