You could try using a 15/50 oil, still reasonably easy to obtain,but to be honest it won't help much, nor will the magic gloop that you see sold on ebay which allegedly rejuvenates tired engines.
You need to find out why it's burning oil, so what you need is a wet/dry compression test, which any garage will be able to do for you. Alternatively, spend �15 on a compression tester (only the price of a can of oil) and check yourself. Then you'll be in a better position to decide what to do.