Voluntary National Insurance payments

Im disabled with progressive MS.  I have one more year's worth of National Insurance payments to make in order to be able to claim full penson when I reach retirement age.  I was advised that if I went self-employed this would be cheaper (Ive not worked for 5 years but was then employed and after this I made 2 years worth of full contributions as if I was still employed.  Last  year I went Self Employed as someone locally was prepared to offer me a role working from home - however, unfortunately this did not work out as the contract was not suitable. (they had no experience of contract law and I was advised not to take it under any circumstances).

This leaves me with a self employment UTR number (which is great) and Ive been advised to pay my final National Insurance year using this as it is cheaper than if I was employed.