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Oh, you sweet summer child.
"Thinking Like A Romance Writer: The Sensual Writer's Sourcebook of Words and Phrases"
This is the book you are asking for. Now forget it because you don't need it. You have all the words you need in your head. Unless you are still operating on a 6th grade reading level (which if you are interested in writing I assume you are a little more advanced than that) you have everything you need, you just have an issue with putting them together the right way.
Let me show you:
Jonas pressed Emily against the wall of the shower stall. The steamy water raining down drenched Emily's too-thin blouse, letting the blue lace bra seep though from underneath. Emily felt his strong hand glide up the inside of her thigh until it grazed her silk panty covered apex.
"Are you going to take all day," Emily teased, "or are you going to fuck me so I can't remember my name?"
Jonas grunted, and with a swift jerk of his hand he tore the thin fabric that covered her slit. She moaned and felt the moisture of her arousal mix with the steam of the hot shower.
Her fumbling fingers tore at the zipper until she parted the wet fabric, and his large rod sprang from the prison of his wet trousers. She marveled at the size, but before she had the chance to wonder if he would even fit inside her, he turned her around so that her plump ass faced his engorged cock. She felt his tip spread the folds of her pussy and...
Well, you get the idea. None of the words I used were anything special. It was all in how I used them. So if you want real writing advice that you can actually use, here is the first one. Fifty Shades of Grey. Nothing in that book is anything special. You could probably write a better book in your sleep if you had half the gumption, and yet it probably is the best selling erotic romance story ever, and I bet you anything E.L. James didn't even break an 8th grade reading level at best. Take that notion of not having the right words and dump it in the trash. You are writing erotica, not trying to get awards from a poetry contest. You have all the literary tools you need so don't overthink it.
But you don't know enough about the craft of writing and you think everything you write sucks? First off, take a gander at this site. The bar is set kind of low here. Look at the top 100 erotica on the amazon. Bar is low there too. You can probably outdo half of them in skill right now. However, you can be better.
1) Go on the tubes of Yu and search for Brandon Sanderson. He is now your sage, and watch his playlist called "2020 Creative Writing Lectures at BYU". Watch it several times. A year. Learn all he has to impart, because a sexy story is still just a story. Get the story part down first and 90% of your problems go away. If you want to know where most of the suck in your writing is. it is at this stage. Thesauruses and word lists will not help you at all. It is in the storytelling fundamentals that you will find your salvation.
2) Now that you have the basics under your belt, travel up the amazon and look for "How to Write Erotica: A Beginner's Guide to Writing and Publishing Short Erotica" and "Romancing the Beat: Story Structure for Romance Novels". Learn the specific story structures for steamy stories.
3) Read, read, read. If you want to write good kissing stories, you need to read good kissing stories. That means finding authors who you like, reading their books and figuring out what you like and what you don't like. I read Eric Vall, Logan Jacobs and Aaron Crash, but there are a ton of good writers, so find the genre of naughty tales you like the most and make a short list of 3-5 authors that you wish you could write like.
4) Get over yourself and start writing and posting your trashy romance stories here. The people who read on this site in particular are so starved for smutt that they are overly forgiving, and most know how hard it is to post your heart and soul for strangers to rake over the coals of biting criticism. Trust me, when you get to this stage, you will appreciate the ego boost, and if you ask for honest feedback you will probably get it... At least you will from me, but even I am too nice here. This is not a professional atmosphere and we don't bite unless you ask really nicely and know the safe word... Which is Fandango in case you were wondering.
Who knows, maybe you will graduate from posting here and try to peddle your (under)wares for coin to off set your steam summer/winter sale addiction like I have been doing under several pen names.
-The Bard ;D