How much should I be borrowing for a mortgage on 85k & is it viable??

Hello :3

I have a question about finding a home and affordability, I'm currently working in London, to I commute once a week so ideally I want to stay near London because of my work I need to wake up very early, and sometimes for emergencies on the day drive to the office to cover someone, so I'm looking for a house to purchase as eventually I want to start a family (early 30s here).

I have saved around 100k for the deposit over 10 years (thanks to this sub also as I have been lurking), so I've been living very frugally but now very luckily and thankfully got promoted, a headhunter came in and my salary 2x to 85k

The most important thing is that I have a good Internet access, I know this sounds really silly but because of my work I deal with very big files that I have to download and upload we get paid commission also on how fast we do work, so I have a three gigabit internet at home, community fibre which is only £70.

Now this is the question the problem is a leased line will cost me over £300 a month 100 megabytes up and down, sometimes more so stupid as it sounds this is dictating where I purchase my house, so I can't move too far away and one of my colleagues moved an hour and half away, and is paying so much for the Internet and having issues with a lease line.

I'm looking for a small house, two or three bedroom, I'm looking to live around Hemel Hempstead, as the prices are a bit cheaper than London and in a nicer area I can get a smaller semi-detached house, whereas Watford and Bushey are slightly too expensive. My biggest priorities are just a driveway, a quieter area I don't mind it not being around travel links so that's why I was thinking this area would be good, of course I would love London but I just can't afford it until a few years.

The question I want to ask is what is a suitable mortgage, I was thinking of purchasing a 450k property, so a 350k mortgage, over a longer term to avoid the high fees, as I am in my early 30s, I'm expecting to potentially sell the property eventually and move back to London when its viable, I was thinking if I also get maybe let's say 35 to 40 years, I could always pay extra and the mortgage back from what I have read in this sub.

I am solo at the moment, I broke up with my boyfriend recently and we are in a "limbo-stage", so I just want to do this myself and not split it with him just in case any future problems, I have been renting in a shared accommodation since after university and I don't really wanna be living in a shared house anymore after saving so frugally for 10 years.

I was wondering if anyone can share their opinion on something like this, I'm looking around paying back £2k a month for mortgage + bills, I was wondering if this is is a good idea and affordable, and was wondering if some other people are in the same boat, or perhaps they would have done things differently etc I don't want to look towards a flat just because of ground rent and servicing fees, also had issues before and unfortunately I cant move too far away because of work it has to be driveable distance near the city.

If anyone has any recommendations or any suggestions please do let me know, I hope I'm not being unrealistic, but I was told I could borrow quite a lot but I don't know if this is financially viable so I was wondering if purchasing a property for 450k and using 100k as a deposit would be a good idea, I don't really want to be renting and wasting the money so I thought this would be the next step forward especially being in my early 30s