Hello GLENNY62: Different people have differing levels of sex drive. And, as a rule, I think it is generally true that men have allot more than women. So, if your wife knows what you're up to, & genuinely doesn't mind, then perhaps there's no problem.
I suppose the question is, to some extent, does your wife really not mind or is she just saying that? If the latter is the case, then this could at some point become an issue between the two of you. On the other hand, if she doesn't have allot of desire for sex herself, perhaps she may see your activities as taking some pressure off of her. It's really difficult to tell. I think the really important thing here is for the two of you to be able to discuss your feelings about sex & masturbation as openly as possible.
As far as the porn goes, it sounds like you have a handle on what you're doing at this point. However perhaps there is some fear in the back of your mind that, at some point, you may cross a line from which there is no return? I'm certainly no expert on things of this nature. However I do know that fetishes & addictions, such as to porn, can be devilishly difficult to break. In fact I have read posts here on PC written by members who have fetishes, who have said that the best one can do is to find a safe way to accommodate the fetish because you can't get rid of it & it won't go away. I don't know how true this is. But it is what others have written.
It may be that an addiction to porn is similar. You may find that you simply can't, perhaps don't even want, to give it up entirely. But as long as you can view it legally & safely, & your wife is okay with it, then it's not a problem. If, on the other hand, you find yourself at some point being drawn more-&-more into it, then you may want to seek out some therapy services in an effort to help you at least put on the breaks. My best wishes to you.