it is very simple, just downgrade sizes. you don't need poppers really but if you like the different kind of high from it I won't stop you. on my case I prefer sober anal since poppers exhaust me and it does the reverse of what makes anal good for me. feeling full from bladder pressure arouses prostate - poppers do the opposite and makes my awakened prostate feel less.
tight internal sphincter is not always a negative, it only is if you use big toys but I use smaller ones and only go about 2-5in depth with a harder glass toy or aneros knockoff, the tight anal sphincter acts more of as a guide for me to hit the prostate consistently though it sometimes gets in the way and needs foreplay.
I think I heavily abused poppers since I was following and looping poppers video so I had like multiple >50 hits (including successive small sniffs as in the video), my longest was like 4hr sesh until my entire vision turned greenish and trippy and the following days my vision became desaturated (it's now okay though, no visual damage, but I think I used up all my vitamin B reserves). and now get coughs from few hits but I don't see poppers as gamechanger, it did give me a nice high but it's detached from the usual anal enjoyment as I've already done HFWO and squirting prior which is consistently harder and impossible to do when on poppers. I already get out of breath on fast fucking with glass dildo so I get exhausted on top of poppers.
my suggestion if you still love size (on my case less is more) or just need some alternative you should try cbd/thc/progesterone inserted boofed/anally (why? https://en.wikipedia.org/wiki/C21H30O2 - the slut holy grail) these three should increase sensitivity and relax your ass. another is melatonin powder has a nice effect of loosning my external anal sphincter which I add with oils. I don't use silicone/water-based lube since it would drip and negate the effects of the other stuff boofed plus glass don't need much lube.