I believe, contrary to popular wisdom, you might have to learn how to walk before launching giant rockets at the Mun.
With the whole Jeb business, I forgot there were still biomes we could science out. You have two possibilities: Either adapt the JebRescuer 6+b (or just use it directly) for such an endeavour, or build a new rocket.
If you do the new rocket, try the following, very simple design: First, the lander. Use the same design you've already had: Capsule, parachute, one materials bay and three landing legs.
Then, the last stage. Add a single of the larger fuel tanks to it (no clue what the name is). Add any engine - then test it (probably the shorter engine). Can it lift off? If so, try a less powerful engine and/or larger fuel tank. If it doesn't use a smaller fuel tank and/or more powerful engine. Test until it barely lifts of. Note the handling of the whole thing - it should be comparatively easy to handle.
Then, the first stage. Double the fuel tanks used above should be good. Again, an engine, more powerful than the first one. Same iterative design procedure. You only want it to lift slowly.
Lastly, attach three to six SRBs. Those give you the speed you want to have. Test it again. It works? Great, then add three to six winglets between the SRBs for stability.
The whole assembly should put you in space. Basically, this is something I have seen at the Minmusshot, I believe you try reaching orbit with SRBs only. That does not work, usually, due to their inefficiency. Like in real life, SRBs give you thrust to lift off, get to about 100-200m/s, then the liquid fuel engines take over with a TWR of slightly above one and get you up up and away.