It's fine, it's natural to feel picky if you're looking for when there's so much to choose from
Anyways, if you're picking a Zowie mouse, you basically have 3 shapes to pick from: EC (right-handed, pretty much the same shape as the G403), FK (ambidextrous, low profile), and ZA (ambidextrous, steeper 'hump' on the back than the FK). The EC comes in 2 sizes, while the others come in three sizes (keep in mind that the closest in shape and feel to the Sensei is the FK1+, which is the largest FK mouse they offer).
If the only problem you had with the G403 was size, then the EC-2A would be a good choice as it's about the same shape but smaller. If not, maybe go for an FK2, as it's designed for clawgrip and seems like it'd suit your hand size. The ZA13 would also match your hand size, but would probably feel a bit weird since it seems to be more designed for palm grip (it might be alright if you have more of a hybrid grip though).