Spicy stories with that specific focus can be a real deep dive, because it's often more of a detailed kink than a central genre tag. I've had decent luck on Literotica by using their advanced search and really playing with keywords – think 'bound,' 'restrained,' 'rope,' 'strict,' alongside the usual romance or erotica categories. The quality varies wildly, but some authors there get really inventive with the scenario and emotional build-up.
For something more structured, the 'Dark Desire' or 'Taken' series from various indie publishers on Amazon Kindle Unlimited sometimes feature those elements prominently, but you really have to dig into the descriptions and reviews. Readers often mention specific scenes in the comments, which is super helpful. I remember one called 'Silken Bonds' that wasn't literary genius or anything, but the tension around that particular focus was surprisingly well-paced and intense. Honestly, half the search is sifting through stuff that just mentions it in passing versus stories where it's a core part of the dynamic.