Appreciation of nonmarital contribution for home purchase

My wife and I recently started searching for a home in NYC. We got a real estate lawyer, and when I told him that I likely needed to make the purchase as a tenant in common because I’d be making a substantial contribution of the down payment with nonmarital assets, and he said that it was fine but that likely I’d get only that amount of money back to nonmarital upon selling as opposed to with appreciation (he noted he was not an expert in marital or tax law).

Is that true, and if so what steps do we need to take to change that (eg a post nup)? My wife is onboard with me getting a percentage based on my nonmarital contribution since we likely won’t be able to make a purchase without my nonmarital contribution. Any other options here?