I know you have asked specifically for female input but my wife does not ever post and sometimes it does help to hear things from the other genders perspective so I'll offer a little bit more from a guys perspective.
From what you have written I think it sounds like you two have a fairly healthy and happy sexual dynamic as it is and I think you are right on track and all you need to do is just keep doing what you are doing and it will happen.
Here's why I think that, you admit to being shy and that if it were up to you you would be stuck with the once a week, missionary position, under the blankets with the lights off etc etc. Well the fact is you two ARE working as a team and you ARE experiencing a varied and active and exciting sex life. Your system IS working for you two even though you may feel like you are stuck in a rutt sometimes.
It's very rare that a couple is 50-50 in their sexual adventurism. One is almost always a little more daring and adventurous and assertive than the other and that is OK. As long as noone is being pushed into something they are not wanting to do or comfortable with it's ok for someone to be the instigator.
And from your description it sounds like he is very sensitive to your comfort level and you are consenting to the things he brings up and then when you actually try it you enjoy the activities and are appreciative that he gave you the little nudge you needed to make it happen.
IMHO I don't think either one of you needs to make some grand announcement that "THE SWINGING MAY NOW BEGIN!" It is all just a process that takes place and I think the process is working for you two. Just let it happen naturally and keep doing what you are doing and some day when the time is right it will happen.
Oh yeah, and show him this thread as a couple of us have already mentioned
