Gift for Emergency Veterinary Nurse (& additional advice for explaining to my 4 year old in comments)

Hi everyone, sadly our family dog passed on March 31st. It has been the most devastating 4 weeks for our family. I'm still crying myself to sleep every night. She literally made me whole. I was never without her. She even went through college with me in my purse back in the day before having my kids. Everywhere we go it's hard bc everyone knew her, grocery stores, doctors offices, church, you name it she was there. I lost my best friend and soul mate 💔 The nurse who took care of her the night she passed knew her from previous unfortunate emergency visits throughout the years and was very bonded with her. I was so glad he was her nurse that night. After she passed I could hear someone else behind me crying and sniffling, it was him. After I finished being with her after her passing he came out crying to hug me and expressed how big of a loss this was to him as well. We have since spoke on the phone during days I've been struggling and we've emailed back and forth. He told me he experiences a lot of loss but some have a bigger impact and he needs to speak about them in order to keep going with his job. He said Tinkerbell's loss and our family will be with him forever. I have thanked him profusely for what he does, it definitely takes a special soul to do that job. Her ashes are now ready to be picked up and I'd like to bring him a gift. Can anyone think of something that may be a nice gesture? I'm so grateful for him.