I replace all my plastic saddles with bone, and compensated bone where possible. Considering how many guitars I have (and have had) that's a lot of darn saddles!
To fit an existing saddle slot, EVERY saddle I've ever put in required some modification, either in thickness, length, height or angle, and more often than not, most or all of the above.
Having an exact copy of your saddle made only works if your saddle is absolutely perfect to begin with. Most aren't. The height is usually off, too low or too high, some are a little too thin for the saddle slot, some are not high enough on the bass side, etc.
Some years ago I got tired of taking my guitars to my luthier for this work (the expense *might* have been a factor too!) so I learned how to make saddles myself.
It's not hard, but you need to be comfortable using sandpaper. And the right tools will, of course, make the job easier. I rely in particular on my Dremel -- the cutoff wheel makes the initial shaping much easier -- and this little doohickey is worth its weight in gold:
www.stewmac.com
Expensive, yes, but it's paid for itself many times over.
Obviously all this is only worth doing if you're like me (heaven help you!) and have acquired, or plan to acquire, a lot of guitars.
Or if you just like the satisfaction of doing your own work. (It is fun!)
