cool whip or other 'edible oil'-based whipped toppings instead of dairy, 'real whipped cream' is good advice.

Also, while I know it is not tasty, have you considered shaving cream? Buy the 'sensitive skin' type (I like Gillette's, but I hear Barbasol has a good one, too) and it won't even sting the eyes. It smells nice, isn't cold, and rinses out easier than anything else.

I was assuming infidelity rather than polyamory based on the less-than-sympathetic phrasing of the poster's advice.

Polyamory's kind of a tough one for us. We started off as a threesome when we initially got together, but after doing that for a year it ended in a kinda heartbreaking way. Thankfully me and my current girlfriend stayed together, but I think we'd both be wary about trying again, especially for something like this. Basically I'm very happy with my girlfriend and our WAM adventures as is - and there are plenty of video content producers out there fulfilling my desire for more extravagant fantasies

Gallons of KY get expensive. I have made, and mastered this homemade version of it though
Ingredients:
I box (16oz) of cornstarch
2-3 gallons of water depending on desire thickness
Food coloring if desired, otherwise it comes out white, almost like cum

Start to boil desired amount of water. In a separate bowl, empty the cornstarch and mix with cold water. Kneed by hand the cornstarch and water. The cornstarch goes to the bottom and turns into a lump. Break it up by hand until its smooth and the bowl looks almost like milk. Slowly pour mixture into warming water and STIR CONSTANTLY!! Mixture will thicken over stove and continue to thicken while cooling. Continuously wisp/stir and combing the cooling top skin with the rest of the pot periodically. CAUTION: DO NOT USE IMMEDIATELY! It needs to cool down because it WILL burn skin!

Make the evening right, and all about her. Get that perfectly safe, neutral, edible, but not very delicious glop on your girlfriend. You can have sex in it, and it's wild JUST KEEP CHECKING THE TEMPERATURE! Stick your arm all the way in the pot while you refreshen her drink or something...Don't burn her! But make it at least warm and inviting.

Test out a smaller batch and you should be able to tell on your own if she'll like it. Good luck!

I tried to skim through the comments, but what about Methylcellulose?

It falls under all the requirements, except one...it is:

Poured on, and can be as thick or thin as you want
Not mushy (it's smooth if properly mixed)
No sugar, PH Balanced (no issues if it gets anywhere)
Edible (it's EDIBLE, but not "tasty". In fact it's tasteless and literally tastes like the water you mix into it)
Not smelly.

I've used it with my Fiance, and its AMAZING. Super slippery, gives a great wet effect, and it can be colored if you'd like.

I'm sure there is some safe flavoring that you can add to it in very small quantities, but It's used as a thickener in many foods so it doesn't really taste like anything.