Need new bottom fill systern and pan but which one?

Need to replace my dys-functional coupled toilet which I can't get to work properly in spite of several plumbers tweeking with its workings, with a new one .
My problem is : Which one would be best to get without breaking the bank,given that some big players in the sanitaryware business are of late , no longer around .

I'm even considering getting a low level toilet ( Very sorry I ever got rid of the original large low level toilet several years ago!!)

The new one needs the contents to clear the pan on the first flush which my current ones most certainly doesn't!

Suggestions of any names or types to consider which would work effectively would be much appreciated!

What's the problem with the current one? Is it just that the flush is slow/ineffective?

You can replace the internal flush mechanism of most toilets. Have you tried that yet?

Yes, we have put in a Dudley Turbo 88 Dual Flush a fortnight ago and even though it is flushing, its wispy to say the least and has been like this for years ! the toilet brand is a Trent which seemingly is no londer around!