Guessing this is the unit...
That's the AMScope M150 series.
If so, stock eyepieces utilize 23mm barrels (a little smaller than 0.965, which is 24.5mm).
The following link shows AMScope's current 23mm eyepiece lineup. The M150 package included the WF10x (top left) and 25x units.
After confirming your eyepiece format, I would recommend a WF10x, to start. With the stock objectives, you'll have 40x, 100x, and 400x. Spend some time with those "native" magnifications. Get comfortable and familiar with its capabilities and limitations. If you find yourself wanting a view in the 150-200x range, then perhaps a 15x or 20x eyepiece (in combo with the 10x objective) might be suitable. I think 25x is less useful with the M150. 1000x (with the 40x objective) is simply not going to work well. 250x (10x objective) may be pushing it, too. Eye relief will be short (perhaps 5mm).
Assuming the barrel format is, indeed, 23mm, you are not limited to AMScope eyepieces, of course. Plenty of 23mm microscope eyepieces from the likes of Nikon, Leitz/Leica, Olympus, & Zeiss are available (second-hand). -And new is certainly not necessarily "better" than old. Most current offerings from the "big four" utilize 30mm barrels, but old-school premium 23mm-barrel eyepieces are not difficult to find. Other fine brands of yore include Bausch & Lomb, Reichert, Wild-Heerbrugg, Mitutoyo, Meiji, and Tiyoda.
It's possible that the particular microscope you purchased is not an M150, and it may utilize 20mm-barrel eyepieces. If so, that's not necessarily a problem, as 20mm-barrel eyepieces are widely available and fairly inexpensive. They won't be high-end premium eyepieces, but that's fine - it's a student microscope.
A video camera might be another useful accessory, and they can be had for as little as ~$45 (VGA resolution). Decent 1.3MP units run about $60. We used an old Orion Starshoot with our Omax microscope (20mm eyepieces, so the Starshoot barrel simply fit over the eyepiece port), and the 1.3MP CMOS sensor did fine.
Here's a link to the AMScope's downloads page:
The manuals aren't perfect, but they're helpful.
Best wishes and luck.
Edited by MisterDan, 18 June 2021 - 07:25 PM.