I think a variable force Topre is a better idea if you are looking for a low force keyboard, they are very light indeed.
This is probably the case. Personally, I would try both if you can. I like the lightness of the Topres, but I prefer the overall force curve and "springiness" of the Cherry browns. I feel that the springiness of the browns provides a sense of "energy efficiency" as the spring helps your fingers up after the stroke. Topres just collapse since they are essentially (really nice) rubber domes. The spring in the Topres is primarily there for activation and doesn't provide much, if anything, to the switch feel.