Sorry to hear of your plight! You are not alone (small consolation I know) in that many Brits have been caught by the 'double whammy' of i) the Annual Review system (that most Spanish lenders use to reset the rate and mortgage payment and ii) the demise of the £/Euro exchange rate.
Having read the thread on this I can see that a Remortgage to an 'Interest Only' has been proposed to reduce the payment amount. Yes, this is a possibility for you to pursue but note that i) any arrears must be cleared with a 3 month period of wait to clear the record as it were and ii) there are potentially high costs. There is an exception to the latter via a cheaper 'switch' deal where the lender picks up most of the normal (5-6%) costs, but the terms are strict. Also, the Loan to Value will be limited to 50% to 60% maximum.
Bear in mind that, come October 09, you will see a much lower rate being applied to the existing mortgage. For example, it seems that the present rate of 5.95% is perhaps the Annual Euribor + 2%. That's a fairly hefty margin incidentally. Today, that rate should be say 4% so the interest element of the mortgage, assuming no change by October, should be 2% ish less than today. Do you know the make up of the present pay rate of 5.95%?
With only 5 months to go I cannot see that you will achieve much with an 'Interest Only' switch but then this is not just for the short term but also the long term as well. It has to be for the costs do not warrant a change just for a wee while!
Meanwhile, keep banging away at the existing lender and make sure that all communication is followed up in writing - to confirm the conversations!