If you have no equity in the property, you will rather be stuck with a new product from your existing lender - some of which are offering very good deals at the moment.
Given that you will be applying for the mortgage in March, which is not too far around the corner, it might be sensible to make enquiries of your lender now to see what is available, or likely to be available. You could also ask them what their policy is to lending to existing customers who are in IVAs, as they will have to be notified of the IVA whether it is proposed prior to or following your re-mortgage.
As an IVA would probably take a couple of months to put together, it would do no harm to seek advice as to this, and other debt solution options, at an early stage - just so that you are well prepared for when the time is right.
Regards, Melanie Giles, Insolvency Practitioner