I thought I'd comment since i did this recently. I moved in with DP, who had a mortgage, and had spent a lot of money on -mostly- doing up the house. I paid him monthly rent, which he sometimes sent back if he didn't feel he needed my contribution that month. I brought my furniture with me, which was my contribution to furnishings! Purchases after I moved in were joint if we both wanted it or individual if only one of us cared (I own the bathroom mirror!).
After a year, we applied for a mortgage together, and I made a contribution to it from savings. I actually made money on that, because it didn't match his equity. It's a relationship, though, not a business transaction, and we were at a point where that felt ok. It wasn't as simple as adding my name, it was a whole new application, and I was aware that he was essentially giving me a gift, even though I was contributing capital. He proposed right after.
What I'm trying to say is that some give and take is a good thing, you don't have to act like it's all business. At the same time, it's a very serious decision to add someone to the mortgage, so take your time on that. You deserve a return on your investment, not just to protect it.
I don't think it's unreasonable to ask whether he'd like to chip in on some furniture and decorating costs, since he'll he using the furniture. You just have to be prepared for him to say, "no, I'd rather swap half out for my own stuff," or "actually, why don't we redecorate, my treat?".