Get a set of butt plugs and get used to the feeling of being full. There's this set that I got from Amazon a few years back that has small, medium and large all together.
Also, you'll need a good amount of lube to make it comfortable and easier to slip in. For these metal plugs, water-based lube like Astroglide or Wet would be fine. You'll also need an anal douche so you'll be clean and ready for play with someone.
Unless the do—and plenty do! If you REALLY want to understand this (as opposed to just shoving your opinions down everyone else's throat), read Not Gay: https://www.amazon.com/Not-Gay-between-Straight-Cultures/dp/1479825174
Mine was a gift but I did a quick google search and found some (even on aliexpress haha), eg:
https://www.amazon.com/Pretty-Love-3-34-Silicone-Anal/dp/B071R9T8KW
https://lovegasm.co/products/silicone-butt-plug-with-internal-metal-ball-3-15-to-4-92-inches-long?variant=39559162527916
Possibly obvious question: Will using bigger plugs do a better job of warming me up? I have a medium-sized plug with narrow stem, kind of like the middle one here. Would I be better served to find a bigger plug with a wider stem?