Whichever type of bike you buy I would very strongly urge you to buy your bike from a bike shop. They will have the experience, the stock and the resources to help you choose the bike that is appropriate for you.

I help out at a LBS - Local Bike Shop - and frequently have the customer who states that they are returning to cycling after xx years and, btw, they have a back issue, so could they please look at a hybrid bike so they can sit upright. Indeed, in the end they may even end up buying one. But bear in mind that shock from the road is passed up vertically through the seat and can often be more of a problem for you if your back/spine is also vertical.

A road bike, of whatever configuration, will mean that those forces are transferred obliquely to your spine and, as a by-product, lead to a strengthening of your core which can only help.

However, with a road bike it's essential to have it fitted to you. The difference between riding a properly fitted bicycle and one "off the shelf" can be huge, especially for those of us with compromised mobility. Any good bike shop should be able to help you with this.