Hi Phil - I've been thinking about this since you posted it but I'm still not sure I have a sensible reply!
You'll get bored if you just keep doing the press ups, so I think it's a good idea to add some new stuff - while keeping doing some press ups too - no point losing all that strength! There are lost of variations you can try - t-push ups, close grip, etc - google and you'll find lots of stuff.
Chin ups and pull ups would be good. They're really hard! So yes, if you tone down the programme for push ups, that might work well. And add in some bodyweight squats (basically fast-ish squats while holding your hands out in front or above your head - get your heart going) and lunges to work your legs too?
I have a wee workout that I do in hotel rooms etc if I can't get to a gym (yeah, I'm weird): it's 20-30 of the following:
body weight squats
push ups
reverse lunges
side plank (30 secs)
closegrip push up
side plank
mountain climber -
http://www.tryingfitness.com/core-strength-mountain-climbers/I do that three to five times, with a minutes rest between (but no rest between the exercises themselves)
Or do a pyramid - do, say, five each of press ups, sit ups, squats (you can make up your own list, depending what you like), then ten each, fifteen each, up to twenty/thirty/whatever is hard for you, then back down through the numbers - the last five of each will be really hard!