New Mom Son idea
I have so many ideas at the moment but finding it hard fid the time to write it all so if anyone wants a go at this, be my guest:
The simple premiss is that mom, dad and son are stuck sharing a hotel room for the night. Back story could be the usual mixup with reservation so only one room was booked instead of two.
Mom wasn't anticipating son being there so she only brought sexy night clothes or none at all as she was intending to spend some quality time with hubby.
Mom notices son checking her out during her changing in the room for bed. While dad is in the shower getting ready for bed, she confronts son who says that he usually jerks off before bed and he hadn't had the opportunity today and that he's already had a shower so going again will make dad suspicious. Mom scolds him and tells him to hold it in for one night.
The three settle on the king size bed for the night with mom in the middle. At some point in the night mom feels son's erection against her ass but luckily dad is asleep. She tells son to jerk it off and he tries but dad stirs when the bed shakes. Turning the light on to go to the toilet will wake dad up and after some dialogue, mom decides son can simply rub his dick on her ass. Things progress to son fucking mom on the bed next to dad.
You could make it more twisted and say that dad stirs with all the bed moving so to keep him happy, mom quickly improvises and makes out with dad. She tells him to be quiet and ties handkerchief to cover his eyes - to make it kinky. She then gives dad a blow job while son fucks her.
If you are going to write this story, all I ask is that you add some background story. For example: dad and son a have a strained relationship and son has always fancied his mom. Also make sure the mom is in her late 30s and absolutely gorgeous with 34dd tits. Other than that the idea is yours for the taking.