Bass Rider is ultra useful. It allows you to really dial in the volume so the bass is really thick but doesn't ever blow out the rest of the song. It also prevents the bass from ever dipping below the volume you want.. it keeps things REALLY level, its like compression but feels better somehow.

Having a good bass guitar is also a big deal, people don't realize this.

Assuming you have all of that.. I'd look at Logic pro's built in bass amp sims.. then obviously Amplitube which is probably considered the best amp sim.. at least amongst all of the guitarists I've spoken to.

You keep using the word thickness so if I were you I'd use a stereo imager to widen the bass. Just a default setting on a stereo imager is going to make your bass sound like 10 times bigger. Some people might freak out about me saying this, but really there are no rules in production and I do this a lot and it works really well. Expander as well could probably achieve this with more traditional means, and a lot of people are telling you to just duplicate the track and pan them to each side which is old school and will also work.. you're going to end up with more mud that way though, because you have two tracks playing. Cleaner to use one bass track with some type of widening plug-in to make it thicker, but some people really like the double tracked sound and that can help a lot. Another way is to LITERALLY double track the bass. You'll have to record it twice, and make minimal mistakes obviously.. don't just copy and paste the same audio into two different bass tracks.. actually go in and record the bass-line twice and then layer those on top of each other and you'll get way more tone. You can do this with guitars too, and obviously people do this with vocals.