While laying in his hospital bed that night, he decided he would get a nice pair of rain boots for his wife next day.
Long shoes aren't long in that the feet part are long (that wouldn't make sense). Instead, the top part is long, making them into boots.
The reading is a bit weird. Double kun'yomi, so think along the lines of 長い and 靴 getting added together. 靴 is the reading you learned with the kanji, however. It also gets rendaku'd.