your proposal to transfer your existing property to a limited company would enable you to buy a property without the second home surcharge but it would not benefit you financially because stamp duty is payable upon the transfer of the property from you into a limited company and limited companies pay 3% surcharge on such acquisitions or 15% if the property in question is worth more than £500,000. This would negate most if not all of the benefit you are seeking to achieve.
The only way you can avoid second homes surcharge would be for your partner to buy the property on his own.
Some people will, after the purchase completes, enter into a declaration of trust as between themselves to record that one of them owns the property on behalf of both in defined shares and such agreements are legally enforceable, however strictly speaking whilst these agreements do not have to be centrally registered - in deed there is nowhere to centrally register them - they do need to be declared to HMRC as to not to do so would technically amount to tax evasion and SDLT would be assessed on the amount of mortgage debt you assume rather than the purchase price but this is a second SDLT bill and it would be subject to the second home surcharge so it will not necessarily produce a saving. I am aware that some people enter into such agreements and then fail to declare them to HMRC on the basis they do not consider it likely that the arrangement can be discovered, which is probably true unless the relationship breaks down and one party decides to report the issue, but it is not something that could be recommended as it does technically amount to tax evasion.
The second home SDLT surcharge has been made very difficult to legally avoid exept in some very limited circumstances using life interest trusts and the like which would not be suitable in your circumstances. I'm sorry this is not likely to be the answer you were hoping for but I hope it as least helpful in setting out the relevant issues.
Does the above answer all your questions? If it does, I should be very grateful if you would kindly take a moment to rate my service by selecting the 5 stars at the top of the screen before you leave JA today. Your feedback is important to me. If there is anything else I can help with please reply back to me though