Floor standing speakers are an option, and I can see why quite a few people find them appealing. £300 including the amp is not a lot of money though for floor standing speakers if buying new. They need well made cabinets in order to sound good, and that means more manufacturing costs. Unless they are more expensive speakers that have an RRP of around £400, but have had a sizeable discount, I'd really look at getting bookshelf or stand mount speakers if you'd prefer to buy new. Floor standing speakers with an RRP of £200 would be a poorer choice than buying some bookshelf or stand mount speakers for £150.
As you've already got some speakers, you're going to be looking for a certain level of performance that you consider an upgrade worthy for the money spent. That makes recommending something quite tricky. Although the Microlab's are PC speakers, they do offer a good level of performance for what is not a great deal of money. If you were buying a set of speakers for the first time, it would be easier to recommend something.
Different brands have different sound signatures too, and as tastes vary, that also makes recommending what speakers someone should consider, somewhat tricky. Some people prefer the sound of Monitor Audio speakers, for example, another person may prefer Q Acoustics or Wharfefdale.
If you've got a Richer Sounds store in your area, I'd pop along and ask for a demo of amp with phono input for a turntable (possibly Pioneer A10 will be the minimum that has that) and various speakers that fit within your budget. Even if you end up buying nothing from them, you'll have an idea of what brand of speaker gives you the sound signature you are looking for.
