How to borrow from friends famliy [ inflation management]

salaam .

i am wanting to know what the correct procedure would be if wanting to borrow from friends and family whilst taking inflation , the value of money into consideration .

if inflation is 3.75%
on 100k - £3750 value drops per year .

if i pay back £100k back after 5 years i am doing them a dis service as the value of the 100k 5 years ago is worth 115k based on future value of money , am i right in that understanding ?

if i want to pay something to cover the inflation loss in the value of money is there an instrument available ,

i have heard the give physical gold in xxx grams and then do the deal and convert to cash , but it is not very practical .

as besides financing through the islamic banks which charges a higher rate i assume , if borrowing form friends and family , very few people would give up that large sum of cash without a rate for a 5 year period .

the purpose of financing is to buy a commercial property generating a rental income already .