In the interest of genuinely advising you on what you asked for (an alternative) ... I'd have to ask what's the most important thing about poppers to you? When you say you're worried you won't want to get fucked without them, which part is it you need from the poppers? The light-headed rush, or the relaxation of your waiting orifice?
There are topical things (you have to dab them directly on your anus, and slip it in a bit) that you can use to relax or somewhat desensitize the area. That could help with the penetration-without-pain side of it.
If it's the rush you're going to miss, I have no idea. Sex while very stoned (pot, and I mean *VERY* stoned) might get you somewhere in the neighborhood. I know of nothing that comes close to poppers, though. I decided to stop using them because of side effects, too.
What I miss most about them is that right after a hit, if you're already horny as hell, it can transport you back in time to the kind of pure sexual mania I don't remember experiencing since I was in the middle of puberty, haha. Everything becomes maddeningly hot for a couple of blissful minutes. Fucking and cumming is fantastic on them.