You were given good advice at the music store. In fact, there are a lot of good reasons that even left handed people should learn on so-called "right handed" guitars. There is very little learning material for left handed players, and even less tab. That means that standard chord diagrams and tab will be backwards for you. There are far fewer options and models for left handed guitars and it's very rare to find one in a guitar shop. That makes it very hard to try before buying.....something that will mean more to you when you shell hundreds of bucks for your upgrade guitar. Another thing that a lot of new players don't realize is that guitar is one of the very few instruments that even has left hand options. If you ever want to learn other stringed instruments like banjo, fiddle, steel guitar, sitar, etc you'll have to order a custom made left handed instrument...$$$$.
Finally, let me leave you with this thought: you really don't know what you don't know. By that I mean that how the instrument feels before you've learned how to hold and play it is totally irrelevant. It's like a student driver getting in a car and deciding that it would be more comfortable shifting with your other hand. This right vs left argument is one we usually have with lefties who are convinced they need a left handed guitar. You're right handed and this should be a no-brainer. Don't make your life more complicated than it needs to be. Best of luck......
Playing guitar since 1964