Fantasizing about bigger

Just typing this out is making me nervous but I need to hear from other people and don't really want to have this conversation with my friends. I've been married for quite some time and me and my husband have a decent sex life. As well as we can with jobs and children these days. I have orgasms with him sometimes more then one. But the last year id say I have been thinking about what it would be like to have sex with a bigger dick. I know I could simply get a large dildo but I am afraid of how he would react if/when he found it. I would never cheat. I have also seen sleeves online but don't know how to have that conversation. Not sure if there is someone who has been in this situation or is this something I should just try to forget about?