Dutch warmblood cross thoroughbred?

I might be getting a Dutch warmblood x thoroughbred, she will be around the 16hh mark. i am unfamiliar with the type as i have a dales pony. if anyone has a dwb X tb and knows roughly what size saddle i will need that will be a big help. i know every horse is differnent. i just need to know whether its worth holding onto a saddle i own, which is a 17.5in wide jeffries falcon hawk event. thanks