Over the past year we have changed over to LED in several of our buildings. The buildings that have suspended ceilings with drop in fixtures we simply cut the ballasts loose. You can then connect all the wires on one end coming from the tombstones to the hot and all the wires coming from the other end to the common. This requires LED bulbs that are duel ended. A lot of bulbs today come combined duel and single ended. With these fixtures that have a diffuser, you can use bulbs that are clear (you can see the LEDs). Our tenants seem to prefer 4000K bulbs.
In the buildings with 8' strip fixtures, cut the ballast and wire hot to one end and common to the other. We generally use 4000K bulbs where you cannot see the LEDs. If we are doing a warehouse we use 6000K clear bulbs. The light is great. You should also install the little clips in the center of the 8' bulb so it does not sag.
I get all my bulbs on Amazon where the price is far lower than going to a regular store. I personally do not think much of the 4' all in one fixtures the big boxes sell. They are cheaply made and non repairable it seems.
I have yet to purchase tombstones. Personally don't see the point. Using 3500K bulbs largely gives you the same lousy light you get from the old style bulbs but if you are into really soft lighting I suppose it works.
The big difference is in the electricity usage. While LEDs do draw power, as opposed to running the old style fixture, they draw nothing. Take out the heat the old bulbs and ballasts generate as reduced load on your A/C and the savings really grows.