I have fitted loads of nuts! I always use Graphtech, black TUSQ, but that is my preference. They are pretty easy to fit, but you have to be prepared to take a hammer to your bass, knock out the original one, take the new nut, check the slot heights, shim/ sand down until the heights are perfect, and then clean up the edges of the nut which are probably too long. If you want I can give some advice on this, I may even make a YouTube video!
If your not overly confident with the above, then just buy the nut and take it to a reputable guitar tech. I do mean reputable as I remember taking my Les Paul to have its nut changed (as well as pickups installed, I was young and scared of doing work) as the E string was buggered. They just filled it with resin. Stupid! The sonics of doing that are bad, and I found out later as I learned more that the overal but height was too low. I eventually changed the nut myself this year and it is now perfect. But yeah, ask around for advice, ask teachers and musicians at open mic nights. Rare and Vintage shops usually deal with a good tech.
So here are what I would see as your options:
A) Graphtech TUSQ. This is fake ivory, and is meant for vintage or acoustic instruments. This material is used on Gibson Thunderbirds, enough said.
http://www.graphtech.com/products.ht...2&CurrencyID=2
B) Graphtech Black TUSQ. This is not as sonically good as the normal white TUSQ, but I like how it sounds anyway. The BIG advantage of this material is that it is designed for tremelos, so is very 'slippy' (solid lubrication). The strings just slide back as you play them. I often pick up a bass with one of these nuts in and it is still in tune after a week or so. Very cool!
http://www.graphtech.com/products.ht...2&CurrencyID=2
