1st off, if you are going to buy a new TV then it is probably going to have to be a flat panel one, either LCD or plasma (that's the 2 different technologies available at present). Unless of course you would prefer to buy an old style CRT TV, which is what you have now. These are the ones with the big tubes out the back, and which are very heavy.
You can still get these but they are becoming harder to hard new. There should be plenty in the 2nd hand adverts.
If you are using an internal portable aerial and have no plans to change then I would not recommend getting an LCD/Plasma TV. These need to have a digital input to produce any decent picture. This will only come from a satellite on your roof, or cable TV. If you try to feed them with a small aerial then you will get a truly awful picture. These TVs are specifically made to show high definition and/or digital signals, and are useless with anything else.
If you have got aerial points on your walls then you may be able to get an aerial mounted on your roof, which will make a difference in terms of quality of signal getting to the TV.
Anyway, I would advise getting a 2nd hand old style TV and sticking with what you know. I think maybe LCDs, plasma's and high definition is a few year's off for you. You'll pick up a bargain in the classifieds. Don't pay more than €100 for one up to 28inch, as no-one wants them and sellers have to give them away. Someone may even give you one for nothing if you pick it up. Thats how out of date these things are!! (I still own a 36" Panasonic by the way, which will be staying with me for a while, as I haven't bought the HD lie yet).