Which pet do you think is good for me?

Have you thought of finding somebody to trade with? You could trade your hamster cage & stuff for their guinea pig equipment. Trading sites you can look at are: Barterquest, Swap-It-Now, SwapThing.
   
BarterBee checks their posters' addresses for verification.
   
You can always buy equipment second-hand & cheaper.
   
Gerbils are good - you need two because the like company, 2 girls are best. They're friendly, are awake part of the day & night, fun to watch. They can use hamster equipment. They live about 3 1/2 years. (Buy them from a private gerbil breeder, they have healthier animals.)
   
What about a parakeet? Or some other small bird? Bird equipment isn't too expensive. You may be able to buy some second-hand.
   
Get books out of the library on Guinea pigs, gerbils, & parakeets.

Thank you for your helpp :) I really appreciated.

Also, if you end up not able to get something bigger than a hamster, then get gerbils (actually, get 2 gerbils).
   
Gerbils are far more sociable & tame well. They actually NEED company. The best pairing is two female gerbils, as they're less likely to disagree & won't have babies (I had 3 girls together, they were happy). Buy them from a gerbil breeder, NOT a pet shop. Pet shop stock is generally too inbred. The gerbils from a breeder will cost more, but be better pets (get litter mates). (Search "national gerbil society uk" to check for local breeders.)
   
They also have a different sleep cycle. They'll sleep for awhile, then run around & eat & play awhile, then sleep again, unlike hamsters - who tend to sleep all day & play all night. Gerbils are also totally curious, unlike hamsters: If there's a weird noise, the hamster will be likely to dive for cover, but the gerbils will pop out of their nestbox to see what's going on.
   
I find them very relaxing to be around.
   
ANOTHER THOUGHT: Have you considered a dwarf rabbit? House rabbits are very common now. The U.S. House Rabbit Society is at "rabbit" dot org; they have full information on keeping bunnies in the house. I don't know if the U.K. has its own society.