Future Loan App and FTB - Looking for Advice

FirstTimePlx

I am a first time house buyer and once I have bought the house, I am looking to do an extension which will cost approximately £30-35K.

I currently have a loan of £15K at 13% with the bank at 60 months (high street bank).

I have had a look at "potential rates" through the bank "offers for being likely/very likely/unlikely etc" for future consolidation or additional loans.

I was looking to get an additional £20K and with consolidating the current £15K (£35K in total) at 60 months/ 5 years the interest rate is cheaper at 9 or so%.

I am currently renting at the moment, (£25k in credit cards with £0 total debt on them) and will be waiting past the 6 months of the hard mortgage credit check.

Unfortunately I don't want to risk putting the new address or any potential quotes on Experian for unsecured loans of individuals whom are home owners.

Are the % rates cheaper for home owners?

My Experian rate is Good.

Looking for some advice.

I have been informed that a secured loan is unlikely due to the LTV of the home.

Is it also better to go to a high street branch and apply for a soft credit check for personalised APR, I have been stung by post office loans before. Where they advertised 95% chance of being successful at 3% advertised, which increased to 12-15% after the hard check.

Thank you