If the goal is 'no IMS worries' and confidence that it will last, I would not source my own bearing. A couple other issues with sourcing your own are that the shop will probably not want to install it and the original center bolt will be compromised after removal.
You can buy the Pelican Parts IMS kit if you want to be cheap. You can even buy it just to get an improved center bolt.
If I was paying a shop to do the transmission repair, I'd go ahead and have them install the LN dual row bearing. Also I'd do the coolant tank if it hasn't been done already.
That said, I was just playing with a 2.5L engine with over 180,000 miles on it and after looking at the bearing I decided to pull the outer seal and leave it alone. At this point the IMS bearing is only one of many things likely to fail and I'd rather replace the engine than rebuild it.
