You may want to get an inexpensive mtn bike and swap the stem out for one that gives you a more upright riding position. You can put
smoother tires on it for riding to work. I prefer not to be so upright but most folks who haven't ridden in years are more comfortable that way. Its hard to give someone advice other than try a few different bikes and see what you like. Make sure you have fun with it whatever you decide. Good Luck!