I wish solids made babies sleep. Because then my 19 month-old wouldn't still be waking 3 times a night even after finishing a ginormous bowl of mac n' cheese, plus some grapes and peppers and cheerios and whatever else she ate off the floor before bed last night!
Thickened feeds (I.e. cereal in a bottle) are something people on this forum generally seem hesitatant to recommend, because cereal in a bottle is a choking hazard. However, I know that thickened feeds are sometimes recommended for babies with reflux. If you want to try it to help with the reflux, and the doc recommends it... IDK, maybe someone else will chime in with better advice on that part of the equation!
Honestly, I think 4-6 night-wakings is in the normal range for a 5 month old baby, reflux or no reflux. Solids might be the magic trick that makes your baby sleep better, but I wouldn't count on it. I personally would attack this issue from the behavioral end- check out Elizabeth Pantley's book "The No-Cry Sleep Solution" for gentle methods that can help a breastfed baby sleep for longer and more independently.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"