Again, a lot of is used a lot by natives !!! Other options are ... Many ... mass of ... loads of ... a large quantity or number of ... a large amount of ... ... in abundance a pile of ... quite a few a good/great deal of ... much of ... huge amount of ... tonnes/hundreds of ... COLLOQUIAL mountain of ... truckload of ...

Let's say you are writing about a potato farmer who has a lot of potatoes. He has loads of potatoes. He has heaps of potatoes. (Australians, especially, use heaps a lot.) He has ton(ne)s of potatoes. Those are the three I would use the most. Here are some more: He has a huge supply of potatoes. He has dozens/hundreds/thousands of potatoes. He has a bucketful of potatoes. (colloquial) He has a truckload of potatoes. (colloquial) He has a s***load of potatoes. (very colloquial) He has more potatoes than he knows what to do with.