2003 W209 CLK, 2005 R171 SLK, Volvo XC40 P8 Twin Motor Pro EV
Heated seats can be quite complicated. Might need a loom as well as switches, heating pads etc.
Parking sensors much easier. MB kit is pricey but aftermarket ones can look just as good and work very well.
The phone really depends on what you have. Many cars have the button on the steering wheel but lack the optional phone kit/module. Look in the centre armrest. If you have a little black connector then you have the optional phone module and you just need a cradle for your phone or bluetooth connector such as the Viseeo MB2