I dived into the foot wells of my GTI and had a good look.
Turns out that the bulbs themselves are just regular 501 or W5W bulbs on their sides.
I am using these at present and they do give a gentle white glow.
However to get a better light cast I would highly recommend replacing these with a white led bulb as in the picture below.
I have borrowed the image from an eBay seller called Super Lights, so all rights go to them. The led is only on one side so the light is directed sideways instead of out of the top - if you get my drift.
To remove the bulb holder/lens assembly are the hardest thing about the job, I would suggest just reaching under the dash lower panel and getting your fingers behind the assembly and pushing downwards, this will result in the the light unit dislodging and allowing access to withdraw it from the whole.
From here you can disconnect the wiring plug, the gently unclip the white backing cover to reveal the bulb.
As many if the experienced modders are aware, you simply lift the bulb towards the side to remove.
Then it's a case of replacing the bull with the led (facing the clear lens), and reassemble In reverse order.
The result is a nicer white footwell glow instead if the dirty yellow that resided there before.
Any questions, just ask.