A lot of DIY jobs are little things like curtain rails, shelves, screw eyes for the washing line.
You will need a hammer drill for bricks, but an 18v cordless will be adequate for small jobs. They call it a "combi" because it can drill, hammer, and (by adjusting the torque) drive screws. I find an 18v is not too heavy even when drilling above your head, and has adequate power for small jobs. 12v is cheaper but weaker.
Unless you want to spend for a tool that will last a DIY lifetime, IMO a big-store own brand will do. They usually have a 2 year guarantee, so use it enough to get your money's worth. Get one with two batteries so you can have one charged while you are working with the other. They are pretty sure to be Li-ion (sp?) batteries now which will last a few years.
A couple of examples of low-price ones:
www.screwfix.com/p/titan-tti699com-18v-1-5ah-li-ion-cordless-combi-drill/4908p
(Titan is very much a budget brand.. but I have some)
So are Aldi and Lidl tools, but they have a good refund or exchange policy.
www.wickes.co.uk/Bosch-18V-Li-ion-Cordless-Combi-Drill-with-2-Batteries-PSB-1800/p/132176
I can't see a Wickes own-brand that fits the bill at the moment.
You can spend a couple of hundred if you want, but the batteries will probably fade long before the tool is worn out.
Toolstation and B&Q will have something similar.
Get yourself on the Screwfix mailing list and they will email you when they have a special offer day (most days with a "Y" in them)
If you ever have a lot of drilling to do, such as flooring a loft or building a shed, a basic mains drill will be cheaper, more powerful, more durable, and not annoy you by getting a flat battery.
If you need to drill large holes, or into concrete, you will need a drill that will be more expensive, or big and heavy. As Thumb says, SDS+ is a different system and not really suitable for light work.