I don't think there's anything which doesn't fall into the category of porn - even 'soft' porn - like the cars/'babes' website www.maxpower.co.uk - that would be accepted by all mums. It's just a few steps away...
I can think of none where women are treated on a par with men (too many use dialogue which shows contempt - I hate the use of words like "tart" and worse).
However, even acknowledging he could look at MaxPower is one or two steps away from porn such as could be found on xhamster.com so it is a real problem to suggest anything.
What do you think of the MaxPower.co.uk site ?
If I told you it used to have a series of questions on the profiles of the 'babes' - things like "What pisses you off about boyfriends?" "Which football player would you shag?" - would you have disliked it (more) ?
MaxPower photos are closer to Page 3, with some 'courtesy of Zoo' etc, but MaxPower makes a point of hiding nipples [but looks like someone with a biro was doodling really - just looks silly]). At least MP has toned down the profiles a bit to remove 'favourite position' 'spit or swallow' and other TMI stuff, perhaps because other sites (agencies and studios) would have vetoed submissions otherwise.
I'm not a cars fan (don't drive) but came across MaxPower when a client's son's PC had various viruses on it (downloaded from some Spanish website giving 'cheat info' for computer games, but also carrying ads for straight and gay porn sites, ringtones, etc)
5 years ago it might have been one to be on the 'ban' list but is pretty 'innocent' now. Never had full frontal, and I doubt you'd see anything more than some naked bottoms (though cannot guarantee it, as I've not studied the site in great detail). I think a change of ownership caused this (Bauer Media seems to have bought it from EMAP).
The ones which satisfy education are generally not going to be that enthusiastically received, and then there's also the legal issue.
Whereas your son's friend telling a lie about being over 18 to gain access to some website is for your son's friend's parents to deal with, I could not suggest buying one of the "Lovers' Guide" DVDs at Poundland for a quid, because you would be breaking the law, if it ever came out.
Incidentally, I have not bought any of the DVDs to know if they are good / bad but it was just to point out there may be items available locally, though in any case, he could not (legally) buy one himself, and you could not (legally) buy one for him. Of course he might 'find it lying about in the house' and be curious...
IMO something like one of those might well be erotic whilst educational. 'Ben Dover' later went on to do his own series of mucky films, but from memory was in one of the Lovers Guide sections as he is, um, well endowed, shall we say...