The 26mm in that scope gets you only 26x for magnification (assuming you have the 700mm focal length 80mm model) which is much less than needed for decent image size on Jupiter. For a scope that size, you could probably handle 120x -140x without losing decent image quality. A 5 mm or 6 mm eyepiece would get you there. (See my article Telescope Eyepiece Questions
for more info on eyepiece math and more.)
Yes, you should have also gotten a 9.7mm (72x) SP, according to Meade. That would be basically a mid-power eyepiece in this scope.
The Series 4000 are actually the same basic eyepieces as the SP supplied with the scope, but with metal bodies and more robust construction. The Series 4000 plossls have long been the standard in a $50 Plossl.
What I would do, here, assuming you can round up that 9.7mm eyepiece, is go with a 2x barlow, such as the Meade 126
. When used with the 9.7mm eyepiece, you'll get a very reasonable magnification of 144x for viewing planets. That's about as far as you want to push an 80 mm achromat in this quality range if you expect any kind of image quality.