siy - you said the magic words "NCP3170. This IC about 1/4 of the price of LM2734Y" :-)
The LM2734Y is a bit more than double the price of NCP3170 at Farnell. RS don't sell the NCP3170
If it is a daughterboard, I don't mind if it gets bigger. Is there an online design tool for the NCP3170?