Thanks for writing. "Think I'm In Love" is actually a Mustang, using an MXR Bass DI straight in. Just so you know. But anyway, yes. A lot of what I rely on is P-Bass/B15 love. Mutations, Sea Change, etc.
I've always heard fantastic reports about that Bergantino cab, particularly with tube heads.
However, yes: I'd suggest you go B15. Or even just anything with 15's. They impart a certain type of mids that I find cannot be replicated otherwise. There's tons more great stuff too: You may want to get into the concept of lower-powered tube amps: B15's obviously, Ampeg V4's, vintage Fender Bassman (or that new 100 watt one maybe - those sound pretty cool), Peavey Classic 50 410 combo (I LOVE those on bass!), Traynor BassMaster II, Sunn 1200S, etc.
You're just going to get so much pleasingly thick harmonic content in those amps, particularly with 15's. Another amp that I love which I seem to use a lot of now in the studio is the Fender Bassman TV 15. I laughed when I first saw it when Fender sent it over to the studio, but man...it records like a dream. I used it on the recent Garbage album, some new Beck stuff, and also the new Paramore, Young The Giant, etc. It's just a solid state combo. But I'm telling you, that thing has magic, recordable tone. Takes pedals great, too. Not sure if they make it anymore...
Now, another thing I recommend is to really get into microphone experimentation. Don't be afraid of 57's on bass amps, especially if you also use a DI to round out the tone. Or large-diaphragm condensers a bit further back from the speaker.
Then there's drive pedals, and that's a whole other thing.
But get yourself a dirty tube amp that you can turn up loud, and you'll be loving that.
Jerose: "Don't forget LEDs!...you need enough to effectively render an assailant blind...once he's defeated you can reward yourself with Pez".