The majority of root canals will need crowns eventually, so it's always better to get them sooner rather then later.
It somewhat depends on which tooth it is as well.
If you get a root canal and just get a filling over it, if it's a back tooth (molar, premolar, pretty much any tooth you can't see when you're smiling) it's going to have bigger roots, and it's also a "high traffic area" in your mouth, meaning you're always biting very hard on those teeth (especially if you're a grinder or clencher, even worse!). Once you have a root canal the tooth slowly starts to dry out, and if there's just a filling on it there's a higher chance part of the tooth can crack, the whole crown of the tooth can break off leaving only the root, or a crack can go down the root, some meaning you'll need a crown done afterwards or else you'll need the tooth out.
If the tooth is semi-close to the front of your mouth, no you don't put as much pressure on it on a regular basis so it might not crack as soon, but it'll still dry out and eventually turn a bit grey-ish, and eventually you might need a crown or it'll crack to the root and you'll need it out.
See the problems here? If you get a crown now it helps preserve the tooth and spreads out the impact points and pretty much prevents you from needing the tooth out (as long as you keep up with cleaning around it and such, don't want any cavities around the borders!!)
Moral of the story: If you have the money or insurance to pay for the crown now (aka if it's in your budget) it's best to get it done because you don't know what's going to happen in the future and if you just get a filling now, when you need something else done to the tooth you'll have already paid for the filling and then you'll have to pay more for the crown or the removal. More worth it to get it all figured out initially.
Hope this helps!
Don't worry about the small root canal thing. Sometimes the actual "canal" (small area where the nerve is) just happens to be small, that doesn't change anything about the procedure.
Also, since it's a back tooth I'd definitely say a crown is the smartest thing to do now instead of waiting because as I said before, if you wait for too long other problems can come up that cause more money (keeping in mind if you needed to get the tooth out due to a crack you might also then consider getting a bridge which is even more money and more difficult to keep clean!)
I'm a dental hygienist. Parents are both dentists.