Hi OP,
I haven't had a drink in 5+ years, preceded by another 3 years of various sober experiments. I think I may have stopped for reasons similar to yourself.
I never questioned the role of booze. I went from university binge drinking to an expat city in my twenties, nearly all socialising involved drinking. I am in a country where people still occasionally express surprise that I don't drink At All - not even a glass of wine? Champagne? What about Christmas? New Year?
First of all, I have NEVER regretted giving up booze. It does change your social life because you lose the acquaintances and the hangers on and the people who think you are "just hilarious". However, you keep the people who matter and the people with whom you have a solid bond of friendship, a shared history, or are able to have an honest conversation with. You also find that your patience for different social situation or for very drunk people changes - I still go out to bars and enjoy parties, but I won't be there until 3 am while some idiot spit talks over me about what a cow his third wife was.
Also, no hangovers ever again. No dread at what you might have done/said/spent. No post-binge anxiety.
Read The Unexpected Joy of Being Sober by Catherine Gray. Or it you think your drinking is anxiety driven, Quit Like a Woman by Holly Whitaker.
In practical terms, start telling people now: "I felt really great during Dry January I am trying to carry it on." Just let your friends and family know between now and the Hen Do that you've found a whole lot of new energy or feel more clear headed, so you'll be avoiding drinking at your parties.
Stock up on Nosecco, Square Root make non alcoholic cocktails in cute little bottles that you can order for delivery. Plenty of breweries make 0.0 beers, although these aren't hangover free as a lot of the preservatives and flavourings are the same. No one can tell the difference between a Mojito and a Virgin Mojito, same with a Moscow Mule or a Tom Collins.
Elderflower cordial with fizzy or soda water is a nice alternative to coke/fanta/squash, and feels more grown up.
If it helps with the motivation, ask yourself "what would I rather do tomorrow?". Surrounded by expats, Thursday night lock ins, Saturday nights out and Sunday Fundays, I was often just drinking by habit or default. I stopped because I felt that being hungover and useless was life limiting. When I was trying to break that habit, I would ask myself "what would you rather do tomorrow? Hangover or go for a swim? Hangover or see a film? Hangover or get your CV sorted?" and that helped me focus on what I wanted.