I know a bit - I upgrade old netbooks as a part time money earner. I'm in a similar position and just swapped the hard drive on current laptop. Unfortunately it's a Sony and won't accept a different hard drive, so have also been looking at new ones - and haven't seen anything that grabs me as I like my old one!
If your laptop is 6 years old and overheating, you might not need a new laptop - 6 years isn't that old and it probably just needs the dust blowing out. The cooling fan inside the laptop gets so clogged up with dust over the years it stops spinning properly. Usually it means taking the back off the laptop and using a can of blown air. Using an antistatic wrist band attached to something metal at the other end, so you don't fuse anything with static. The fiddly bit is making sure you don't lose any of the little screws from the back when you've taken it off and that means needing a small screwdriver set that is magnetic (it picks the screws up magnetically and holds them in place).
So basically, if you know an IT person who wouldn't charge too much, and has all the bits and pieces, they could take the back off, blow the dust out (and there will be huge chunks of it turned to a thick layer!) and put the back on again and it'll stop overheating.
I wouldn't suggest doing it yourself if you haven't done anything like that before, and sometimes it's not worth paying someone if the laptop is getting old, but it's quite a simple thing to sort if you know an IT person who'll do it for £20 say.
Some laptops are easy and it's just a case of taking the back off - some are too difficult and need to be almost totally taken apart (if you google the dissassemble instructions for your model it will show whether it's an easy one or not). You can manage without an antistatic wrist band, by just leaning against a radiator when you do it or wearing rubber soled shoes (proper rubber). But I wouldn't want to do it without the little magnetic screwdriver set - mine only cost £2.60 from Boyes
And a can of blown air. Static can kill a laptop.
You have to blow the air from the inside, so the dust goes out through the vents. If you try blowing the air through the vents from the outside, it'll all just go in and over the other interior parts of the laptop and cause more problems, so it needs the back off really.
We only ever buy used laptops, because new ones are so expensive! But then I can upgrade them easily. There are some good deals on chromebooks - which aren't too expensive. It depends what you use your laptop for. Chromebooks are basically for doing everything over the internet. You don't download and store things. That doesn't appeal to me - I like downloading and storing things, but a lot of people use cloud based storage for everything. I wouldn't get a Sony again (you can't now anyway, they've stopped making them!) - it's a lovely laptop but it's the only one I've ever had that won't let you upgrade the hard drive - some hidden software they put on it I think. So if you're hard drive dies (which mine is about to) you are left with a useless computer you can't fix!
What kind of things do you do on your computer apart from go on the internet? Anything with an Atom processor (smaller netbook types) will be very slow and you wouldn't be able to do video editing. Likewise anything with a Celeron processor or AMD processor. You'd need an Intel i3 processor if you want to do anything like video editing. If you don't do things like that any laptop would be fine and you can put more ram in it (very easy) to make it go a bit faster.
If I had the money I'd get a 13" Macbook Air - but I don't lol. It's fast does everything, has a better keyboard and ergonomics than the macbook or macbook pro, but costs nearly £1000 and you're limited to 250GB storage.
This page has suggestions for best budget laptops 2016.
13 best budget laptops 2016 UK: Best cheap laptops you can buy - Test Centre - PC Advisor
Their number two - the Asus sounds like a good all round budget laptop. It has a reasonable processor, 1 1TB hard drive - ie 1000GB (which is huge - you would never run out of space). When it says slow wifi and poor resolution graphics it just means they are bog standard and not like a mac. Most laptops have the 'slow' wifi which is just standard wifi - it's all I've ever had - it works fine. Low resolution screen means it doesn't look as glossy as an ipad. I've always found Asus laptops reliable as well and you can upgrade the memory (you can't upgrade anything on the HP laptop they have at number one.
Asus X555LA-XX290H review | best bbudget laptop - Review - PC Advisor
My problem is I prefer 13" or 14" laptops and the best priced ones are usually 15". I just find the mouse pad too far over to the left on a 15" laptop so then you need a separate mouse, but if you're used to an offset mouse pad that shouldn't make much difference.
You could get a tablet with an attachable keyboard. But a tablet will never have the storage space of a laptop and is back to almost being a chrome book again.
I you want a really cheap option, you could buy any cheap second hand netbook and put Linux on it instead of Windows. That's what I do with the netbooks I buy and sell. They are usually on XP and have run out of space to run it (plus it is now obsolete) - but it starts to get geeky installing Linux - which is a free operating system. It runs really fast on even netbook and comes with everything you need but it's a steep learning curve after windows and not as slick, plus your windows programs aren't compatible - but fine for the internet - you end up with a chromebook again basically.