I have made a successful self screen replacement from TN screen to IPS screen, however with some lessons learned.
I purchased my x220 in Sweden, where very few x220 models were offered with an IPS screen. Actually I found only one and that one was about 5000 SEK (about 740 USD)
more that a similar one with the TN screen.
So, I bought one with the TN screen, model number is: 4291-37G.
I then ordered a screen from ebay listed as "LP125WH2 SLB1 Compatible" from the German seller "lcd-displays" for 96 EUR (about 126 USD)
It arrived only a few days later and I installed it according to the service manual - a LOT of steps, the section "2050 LCD panel and LCD cable" lists 11 FRUs to remove before removing the actual LCD cable.
Actually, only one of these 11 FRUs needs to be removed (at least for my model and I suspects it's the same for any other x220 model).
Anway, the replacement took a couple of hours of fiddling, and then I turned on the x220 only to discover that there was no visible difference in screen quality
After e-mailing with "lcd-displays" it turned out I had indeed received a TN screen. The "compatible" apperently does not cater to the IPS tech.
They offered an IPS replacement where I would pay for the difference in price plus shipping. The IPS one was 118 EUR (ca 155 USD) so not that much more expensive.
I bought the IPS model and it arrived two dayer afterwards!
Here is a link to the one I bought (IPS):
http://www.ebay.de/itm/230731242028
Now I replaced it by only the 2010 and 2050 step in the service manual (LCD Front Bezel and LCD Panel and LCD Cable), 2020 LED board not needed to remove.
And voila! The IPS screen is so much better
I can really recommend this upgrade; I guess the hard thing is to source the correct screen depending on where you live.
/Daniel