Hi
The good thing about dating is that you always have a choice of what you want. If you really cannot accept this height and thin issues, then I advice you not to go further than where you are right now. In the meantime, enjoy the godly clean fun dating which both of you have at the moment.
If God has spoken to both of you to consider a serious relationship together, then ask God for wisdom and the grace to accept the man whom God has brought into your life.
Before I got married, I have been a skinny boy right from birth! After marriage, I 'exploded' a little and my wife asked me to reduce a little. Currently, I am skinny again and my wife thinks I should put on a little more. It never ends!
I told my three daughters that I have only one criteria for their choice of soul mate - that the man must always lead them closer to Jesus Christ everyday.
The rest of the criteria, I have asked them to work with the Holy Spirit and of course, I will be more than willing to advise if they ask.