First time abroad with children

Hi, we are new to the forum. Our daughter is nearly 4 and was diagnosed last summer as having ASD. We have two other daughters aged 6 and 9. We have been on a few holidays in the uk with success, now looking to try a private rental somewhere within an hour of the euroshuttle. Prefer coastal or with pool - any personal experiences greatly appreciated. Spent a full week on trip advisor now and it's not getting any easier!