What sort of soil do you have now, what depth do you want to add and what do you want to grow in it? Are you expecting the soil you buy to be heavy clayish soil or light sandy soil? As you have not said where you live we can't guess at that! Peat can be added for two reasons, one to add humus to lighten heavy ground and one to acidify it to make it suitable for plants like rhododendrons and summer flowering heathers.

I know of 3 places that do good online soil of all sorts, the type you order as Steragram says, depends on your needs.

You can probably get "top soil" locally, relatively cheap, tipped in ton loads onto your property. Trouble is, you have no idea what it's origin is.

Or you can pay more for guaranteed quality.

And if you buy locally, then go and look at the stuff before buying it.

I have had several lorry loads delivered as had the whole garden turned over at the end of summer. I went to look first and the provider of the initial supply was not aware (so he says) of the presence of knotweed. Then paid a small fortune for the stuff from a different chap as had to have the whole garden covered, got lots of diverese plants one of which I know to be 'scutch grass' which is bad news, hope when it reveals it's secrets in the Spring I will not have any other surprises.
It a risk and a learning experience. Good luck.