Hi John,
If you are looking for second hand furniture there are plenty of charity shops and adverts in local papers with people wanting to sell stuff. This could be a bit time consuming though. You would be better off going to Ikea. You can choose stuff online first and then go to pick it up, There are even companies who will deliver for you.
You can esily buy beds, garden furniture etc at the hypermarkets and Casa is great for smaller furniture items and accessories.
If you are renting out your apartment make sure the furniture is modern and looks good, this attracts more renters. People demand high standards nowadays so it is worth paying a little bit more . If it is just for personal use you don't have to consider this.
Happy shopping !