Here's my advice: Stock up on Pencil Rockets. I suggest going all out, and buying 3 or 4. Yes, they're 500 DP, but they'll help you in the end.
Also, use PK Love, or whatever you said your favorite thing was, but make sure you don't spend all of your PP on it. Either save some to use on Lifeup, or if you have Magic Gelatin or Tarts, use those to refill your PP. I say not to let it dip below 15-20 points.
If you run out of PP and Pencil Rockets, you should just beat up the Jealous Bass with physical attacks. I suggest going back to the Clayman Factory to get a Good Stick from the Squaking Sticks by the train station. It's got +27 Offense on it. You'll probably need to beat up a whole bunch, though, since the odds of a Squawking Stick dropping a Good Stick are only 5%. Plus, they drop regular sticks more frequently, which are worth 200 DP, and you can sell your Easy-Grip Stick for 1500 after you get a Good Stick. These statistics are from the top of my head, so I could be wrong. I'd look it up on EarthBound Wiki just to be safe.
Yes, I obsessed over this game. There are tough parts, but if you power through them, you will be satisfied. Take my word for it.