If you want to do continuing simulations of the tax return that you will be preparing during the upcoming tax season, I suggest using the CD/download version of TurboTax and using its What-If Worksheet to to that simulation. You can use it to prepare and save on your computer as many simulated tax return as you like.
The CD/download version of 2019 TurboTax is expected to be available in mid-November 2019, so it probably doesn't make sense at this point to buy the CD/download version of 2018 TurboTax to simulate a 2019 tax return; just wait another month for 2019 TurboTax. The online version of 2019 TurboTax is expected to be made available in early December.