My rule of thumb is that if I have to ask myself “would this be going too far?”, it is probably a step beyond where we should be.
I do not think using the “does it turn me on” as the determiner is always the best because if you wait to find out you have probably already crossed a line. Also, there can be totally non intimate things that turn you on. An example, I really like the “country girl/girl next door” type. If they are not afraid to get their hands dirty… even better. I remember one time my then GF, myself, and some others were working tearing down a building on a ranch. I turned around and saw her with her hair a mess, dirt smudged on her face, in loose dirty work cloths and I was turned on by it. I thought she looked fantastic. Another example just recently, I was doing some holiday baking with my GF, and just seeing her in the kitchen which was a mess with flower on her just relaxed and having fun, was a slight turn on for me. I would argue that there was nothing wrong with either of these situations, no one was dressed immodestly or doing anything inappropriate, but the situation still triggered a certain emotion.
I don’t know if there was a useful point to all of that, but I would just say error on the side of caution.