As a retired TA I'll add a couple more ideas:
When reading harder books with a child, get him to point to words as he goes along. If he knows the word, or can sound it out, he can say it. If he doesn't know the word, he can hover his finger over it, and YOU say the word for him. Don't stop to analyse or discuss the word at this stage, but try and keep the 'flow' of reading going. Review difficulties at the end, if you wish to. This way, he has the satisfaction of reading more difficult books, without the fear of getting 'stuck' on words.
For slightly older children I sometimes recommend what I call "Value Added" books, that is they have an aspect in addition to just reading a story.
The best one is Arthur Ransome's "Coot Club" set on the Norfolk Broads in 1930. All the places in the book are actual locations, and can be found on the Ordnance Survey 2-1/2inch map of the Broads. All the villages, rivers, lakes, pubs and windmill pumping stations can be seen on the map. Apart from some railways being closed, and there now being more main roads, little has changed. It also gives interesting insights to the social history of the '30s: the children want to contact friends in a nearby village, and say if they post a letter in the morning, it will get there by the second post in the afternoon! When they buy provisions at a riverside shop, the shop-boy carries the goods down to their boat for them.
Another book in a 'real' place, is "Watership Down". The rabbits' home threatened by development is actually on the outskirts of Newbury, in Berkshire. There are several web sites about the locations, and even guided tours sometimes to places featured in the book.