my site sells contact lenses and customers should buy 2 lenses of different powers for 1 pair.

currently the site is setup to check out one lens at a time BUT lots of customers are forget to buy 2 so I'm hoping I can either

1. bundle two products as one sku

or

2. two attributes per item/pair (one for right lens power and the other for left lens power)

and ofcourse I still need to maintain stock by attributes in that case.

Any recommendations?