Hi there,
Personally I would not start solids in order to get LO to sleep better as it can often have the reverse effect. I am sure you know but before 6 months many LO's digestive systems are not mature enough to digest solids and it can cause more problems and actually increased NW's.
Having said that I did start to wean my DS at 5 months as I felt he was genuinely ready for solid food. He was taking around 40oz of formula and was very interested in what we were eating etc. I started very slow with just baby rice, then fruit and veg and stuck with that until 6 months.
Hope this helps
Becky x