Do we have anything like treasury bills or short-term government bonds with good interest? Something that matures within next 3-6 months...

There is HL Active Savings with 4.3% deposit for 9 months fixed.

But yes, the real yield is of course negative, but show me something with a positive yield that gives the Government protection and guaranteed yield (near enough) with no capital risk.
But I feel like this type of instrument is to address people who seek the capital returned to them for something larger purchase shortly after maturity. It certainly has its place & I use these for situations like this recently.

What do you regard as good?

i keep it on my deposit account. So far i didn't have any issue with the comenity bank and their customer service Is always very helpful (you can find their details by link). Other than that i invest in real estate and am very close to purchasing a second rental flat. Hope to have an independent income by the time i am retired.

Heavily into a range of BG funds, I cashed in everything in January 2022. Too timid for the 'Stay in! The markets always come back!' mantra. On reflection, right decision for me. Interest rates on 'parked cash' - my terminology! - are steadily climbing. In last 10 months, I've moved from HL to II and now to Vanguard who are offering 2.73% on 'parked money'. Not bad for instantly available cash. No need to invest. Vanguard hold over £3trn. Also, many high street banks and building society offering 6-month and 1-year bonds at attractive rates. Or even an ISA. Good rates and tax free on interest. Anything would be attractive after 10 years of meagre interest rates for pensioners. I follow Savings Champion for weekly updates on best interest rate offers.