Help!! How to spice things up

This might be kinda long so sorry in advance lol my husband and i have been together for like 3.5 years and when we first started having sex, things were great. We were spontaneous and things were still so new and exciting and we were doing it all the time. Well the past like year and a half or so my husbands sex drive has gone down considerably. I just thought to myself ok this must really be his normal sex drive now that things aren’t as new and exciting as they were originally. Sometimes we have sex twice a week, other times it’s like twice a month. There’s no telling which it’s gonna be. At this point, i would say, i have a higher sex drive than he does and i try to initiate sometimes but he shuts me down and just says he’s not in the mood. Well last night we FINALLY sat down and talked about it and i asked, “if we mixed things up and it was more exciting would you be into it more?” He said that most likely yes, he’s just like this now because we’ve been doing the same things for 3 years. Ok i totally understand but i try to mix things up and he doesn’t go for it. So i told him, I’m always buying lingerie, sexier pjs or underwear and try to initiate but you shut me down so if you want to mix things up, it’s partially on you too. I said just try to be more spontaneous, surprise me and mix up positions or just let me initiate for once and get you in the mood. He said ok and pinky promised he would try lol

my question is, what other ways can we spice it up? I’m down to try anything, except butt stuff lol, but he’s a little more vanilla. The “wildest” we’ve ever gotten was using a tingly lube and he just said it was “really weird” and we haven’t used it since 🤦🏻‍♀️ I’m open to any and all ideas!! I just really wanna keep things interesting because if we’re already hitting this wall at 3.5 years in, imagine what it’ll be like in 5, 10, 15+ years 😯