How to buy another house before selling mine - Help?!

I currently live in a £240,000 house, which I own without a mortgage. I would like to buy a flat for around £220,000.

I must sell my house in order to pay for the flat without taking a mortgage. I am worried that in the time it takes to sell my house, the flat might be sold to another buyer.

I would be extremely grateful to hear any ideas about sensible ways around what I assume must be quite a common problem.

I have a few potential solutions in mind:
1. Get a mortgage for the new flat which can be paid off without penalty within the first few months (Assuming such a mortgage exists and ideally interest only)? But I am approaching 60 and so payments might be high. Perhaps my son could get one in his name (salary of c. £50k and no debt.)
2. Redemption mortgage on my current home.
3. Buy to let mortgage - from what I have been told, tend to be cheaper and often interest only (and could well be appropriate if I end up renting out the flat until my house sells).
4. Bridging loan? Heard these are very expensive.

Thank you for all of your opinions in advance-they really are much appreciated.

Chris

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