Faulty bed frame but mattress fine

I bought a bed package from Jysk which consisted of a metal bed frame and a mattress. I don't have a lot of money and their package deal was very attractive.
After a few weeks, the welds on the frame gave out and the bed collapsed.
Jysk replaced the faulty part immediately but, after a few more weeks, the welds on the new part also gave out.
I am now sure that the frame is poorly designed and of unsatisfactory quality.
I visited the shop this morning to complain and either get a refund or a more reliable replacement.
The options I have been given by the shop are:
1) a £53 refund for the frame only. The company say they will not refund the mattress as it is now used. £53 is not enough to buy another bed frame anywhere.
2) Pay an additional £150 to upgrade to another frame which will fit the existing mattress. I do not have £150 to spare.
As a result, I am now stuck with sleeping on the floor.
I believe that the company should refund the full cost of the entire package including the mattress as it was bought as a package.
Does anyone know what my rights are in this situation?

Thanks for your reply.
The mattress is a standard, king size mattress and can be used with any king size bed frame. Jysk, however, have very few king size bed frame options.
Yes, they are available separately and, at the time, the bed frame was selling separately for £98.97 with slats, the mattress for £109.00.
When bought as a complete bed set, the price was £169.00.
Those prices have since dropped to £88.78 and £99.00 respectively and a complete price of £159.00.
I know that these are relatively small amounts but, at the moment, every penny counts.