Since it you have already talked with your husband about masturbation, then there is no need for me to suggest that, but further talk may be useful. Is he masturbating while watching pornography on his phone or is he just doing it in the dark without any visual stimulation? Does he have any interests or fetishes that he is imagining but not divulging to you? His lying about it is worrisome, since you've voiced your appoval of masturbation already.
Here is another woman/wife weighing in. Masturbation is easy. Easier than having sex/making love to your partner. I don't think it's a personal statement of his affection or desire for you. But rather his just wanting a quick release without having to cuddle and be considerate of someone else. I agree with you that it is a little lazy to have to stay right in bed to do it with you there. Like, take a quick to the bathroom dude. Maybe tell him that. That you don't care about it but that you really would rather he take it to another room. Heck, you can even say it is disrupting your sleep and that is rude of him. And if he tries to lie, say forget about it. You know so stop with the game playing. Take it to the bathroom or wherever so you can sleep. good luck
You can get him interested in showing him a male deer exercise. You may also do female deer exercise. You may google these phrase, learn details and both of you can practice as a fore play ot to get sexually free with each other. Other exercise is kegel exercise. After you learn this exercise, you can kegel each other and have different sensations.Another exciting exercise can be a peripheral anal prostate massage.Google this massage also. It will be enjoyable good for his prostate.Find out different postures for intercourse. This will give haim different experiences.It is an interesting subject. Post your findings in this forum.Thanks.