Astromania Telescope Eyepiece 3.2mm, Wide Angle 58 Degree Apparent Field Planetary Eyepiece for 1.25 inch Astronomy Telescope & Filter, Fully Multi-Coated Telescope Accessory for Planetary Observation

I wrote a guide on the low to mid-ish range eyepieces here. Note its recommendations for focal length (your "what mm should I get though") assume 1200-1250mm telescope focal length, so that will require some adjustment for your 750mm telescope. Let me think... Shooting for magnifications of around 50x, 80-100x, 125x, and 200-250x I recommend: 50x: 15mm redline or "Dual ED" 80-100x: 9mm redline or 8mm "Dual ED" 125x: 6mm redline (low priority magnification in my opinion but ymmv) 200-250x: 3.2mm "TMB Planetary" eyepiece or the 4mm if you don't go for the 6mm slot. The guide I linked explains my opinions and what I mean by "Dual ED" and "TMB Planetary" eyepiece. This is rather prescriptive and thus may not fit what would actually be best for you. Read the guide for more general advice, and I recommend you stay away from plossls below 15mm, and even that is pretty short.