Hello, im a intermediate 13 year old player. In probably the 8th best in my school. I have been noting the strings on my racket aren't as tight as they were before and im getting less power on my smashes. I have a Yonex Volrix Pegasus with a recommended string tension of 18-24lb. I am a player that likes no loves to smash. Are there any good strings that have good durability because i don't want to keep on spending money on strings, but are also good for smashing.