In my previous car I tried all sorts of HID kits, from £20 eBay specials to HIDs4U premium ones. All of them ended up looking aftermarket-y, some just looked chavtastic (even though they were supposed to be 5000K). So I recommend an LED kit.
I have one right now and I'm very pleased with it, mainly because it looks OEM and has greatly modernised the looks of the car with the lights on -- it's nice and white.
Some photos (looks a bit blue-ish, but it is true white in real life, which I failed to capture with my camera):
The parts you'll need (no need for coding with these):
https://www.ebay.co.uk/itm/For-BMW-E60-X5-XENON-HID-LED-LIGHT-BULB-HOLDERS-ADAPTORS-Replacement-TYPE2/372230952265?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
https://www.ebay.co.uk/itm/V9-CSP-LED-Headlight-Bulbs-Kit-10000-Lumens-12-24v-Canbus-Error-Free-H7-H4/372593012558?ssPageName=STRK%3AMEBIDX%3AIT&var=641361292559&_trksid=p2057872.m2749.l2649
https://www.amazon.co.uk/gp/product/B07FKKDTD4/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1