Tying Private Lending Rate to WSJ Prime Rate? (As the lender)

[James Palassis]

I have been lending for a few years now, with terms anywhere between 6 and 12 months. I've been approached by someone I've lent to in the past asking for a 5 year term. Great history with this borrower, always pays, no issues. My issue is locking into a rate for that amount of time with the unpredictability in the mortgage space right now. I don't want to put a loan out at 12% if there is a chance my premium to risk factor might disappear in the future. 

Examples: 

When traditional rates were avg 3.5, I was getting 10%.

Now traditional rates are approaching 6% and I'm getting 12%.

So I don't want to lock in at 12% and watch my spread erode. As a workaround, I thought about tying my rate to the WSJ prime rate. Was thinking interest only variable rate at prime + 500 bps (5%) with a floor rate of 8%. Prime is currently at 4.75, so the loan would start at 9.75%. Whatever prime is on the 1st of the month dictates that month's interest, and rate cannot go below 8%. 

Looking for feedback on this loan structure. Has anyone lent money at a variable rate for a longer-term loan? Is correlating the rate to the WSJ prime rate a good route to go? Thank you for any feedback.