Conversion of Commercial to Residential, Funding

Hi, looking for advice on the right financial product to carry out a project.

In short, I’m looking to purchase a town house property, currently configured as offices, but sold with permission to convert it to residential 4 bed property. I want to purchase it, do the conversion and then live there in the longer term so this is not an investment/profit effort.

Current advertised price is £300k and I’ve £225k in assets that I can put into this. I’ve a background in the work required and access to additional expertise where needed (Grade II listed…). It doesn’t actually need that much, just kitchen/bathroom going back in to where they were 6-7 decades ago plus stud walls for fire regs etc. but obviously doing with conservation officer okay will stretch timings. Conversion costs I estimate in the £20-30k range, but my plan is to borrow £150k on a 50% LTV and thus have at least £75k available for it. Clearly I don’t want to spend extra if I can help it! I’ll have to contract the building work out, not least as commercial work gets a 5% VAT rate but as a private person I cant buy materials myself for that, so factoring in the time, potentially specialist bits for the listed aspect it makes sense to use builders.

I’m looking at bridging loan which I think is the only way to do this, 6-12 month duration and an Exit to a standard residential mortgage once the conversion is done and the council classify it as such. £150k is bang on suited to my income (armed forces £45-50k but with post-divorce payments).

So far that kind of makes sense to me.

But, is that the only option? I’m new to this aspect of finance (had a standard mortgage before), but they are generally monthly interest (c.0.5%+) but I have seen development loans at a 5% per year – are these also suitable as they seem substantially cheaper and bridging seems designed for short term loans – this is a project that will deliver a fairly defined output, and already has a defined value.

It seems a pretty safe bet given the loan is half of its current market price, I’d estimate £350-400 for the completed value.
Any advice or comments welcomed.