Is it possible you've simply got too many polygons at too early a stage to get smooth curvatures easily?
This illustration may not be exactly what you're looking for, but shows the kind of variation you can get from a Bevel modifier and subdivision:
- Shows the mesh. A 2-segment Bevel modifier is assigned, by weight. The weights on various edges are adjusted to increase/decrease the intensity of the crease after subdivision (The lower the weight, the sharper the crease, relative to the base bevel width set in the modifier)
- Shows the Bevel modifier applied: what it's actally done
- 4,5 Show the result after 2x Catmull-Clark Subdivision.
I haven't gone all the way here - you could apply the Bevel, and go in to tweak the topology to remove any residual pinching, etc.