I live in Cornwall and think in some ways you don't need as much money to enjoy a good standard of living here because so much of the leisure is free (beaches, natural beauty, outdoors lifestyle) or has a relatively low cost barrier to entry (surfing, kayaking, etc). There is less availability of expensive events to attend and no one cares very much if you have expensive beauty treatments, what car you drive or what you wear. Rich and poor spend their leisure time more similarly, on the same beaches, enjoying the outdoors and so in my experience you don't feel as poor as you would in other areas once you've got the basics covered.
Housing can be expensive, but OP has a deposit of £150k which will be very helpful and where I am in Newquay there are 3 bed doer uppers starting from £200K or more done up ones from £250k, a budget of up to £320k would give her her pick and should work out to be a mortgage of about £1000 a month on a deposit of £150k (according to Rightmove) so she'd manage quite nicely in my opinion.
In my experience how rich or poor you feel has more to do with your immediate surroundings and how rich or poor those around you and particularly your friends and family are so I agree with other posters that you should survey your relatives currently living in Cornwall.
We live frugally but very happily on a very low income (but we're mortgage free and no kids so quite unusual I agree). Obviously it depends on what you value, for example I cut and colour my own hair, buy most of our clothes secondhand and as much other household stuff secondhand as possible as well (we just got a new to us cooker for £10 from facebook marketplace) but I don't mind any of that, in fact I enjoy it and would probably do it whatever we earned as I hate to overpay or feel ripped off and the cooker was exactly the kind I wanted and was looking at spending at least £500 on new so I'm really happy with it.
We needed new armchairs recently and I ended up with an as new Ikea Strandmon with footstool for free (again fb marketplace) and the lilac cotton velvet armchair from Anthropologie of my dreams in the sale at a third of the original price. I spent £200 on those two items but if I'd bought them both new and not reduced it would have been close to £1000, when you have less yes you have to cut your coat according to your cloth but it doesn't have to mean you can't still get exactly what you wanted sometimes, you get better at figuring out what that is and prioritising.
Our car was £300 from a friend, it lets the rain in slightly somewhere which ends up in the back footwell but it goes, is cheap to run, easy to park, I don't worry about it being scratched or stolen and it gets me where I need to be so I'm happy with it. Living this way I feel like I can buy whatever I want with a bit of time and searching and OH and I both work low part time hours and mostly are able to do whatever we want, but of course your mileage may vary and it depends on what you want to do.