Kegels and relaxation exercises for sure. For me it's different masturbating or using a toy vs real sex.
For toys and hands, it's much harder for me to go longer, I just dont get in the same state of mind as I do when I have real sex. Toys and hands for some reason tend to be more "transactional" for me, like more about finishing vs lasting.
When it comes to real sex, I have found that getting myself the most aroused I can through foreplay provides me the most longevity during actual sex, like to the point of being so damn hard that I almost cant be made to cum by my wife, she ends up complaining eventually and then tries to jack me off and even then, sometimes I'm so far gone that she cant even make me cum, I have to step and in rub one out on her myself, violently, that or the erection just ends up going down by itself after so long.
I have not mastered how to get myself into that state of mind but the key is definitely maximizing my arousal level before sex. It's hard sometimes, specially after being with the same person for more than 14 years, you have to find ways to spice things up, and its often harder than it sounds, specially if they are not as perverted as you haha
Anyways, try experimenting with getting yourself super aroused before you start to use the toy. It might also help. I think it's because the blood flow probably is very high and your penis is rock solid while the state of arousal is also a type of "distraction" as other have mentioned also helps, anything that distracts me from what my penis is feeling every second is a big help, so the arousal tends to do that for because it puts me in a very "animalistic" mental state and all I am mostly thinking about is how i can destroy this woman with my penis hahahahah and not so much how good it feels.
I would def not recommend desensitizing creams, they do work, and you have to find the right timing and amount to work with you and if you dont get those rights, it can completely ruin your attempt by making it very difficult to get hard when your dick is all numb. Keep trying via the natural way.