You can have the monthly premium bond wins automatically reinvested to buy more premium bonds, so it feels like you’re getting the wins as interest. You do need a significant amount in premium bonds to consistently get close to the current notional 1.4%.
You can use your Isa allowance for an investment (stocks & shares) ISA, which is the best chance of beating inflation, but is only suitable if you don’t need access for 10 years or more.
Coventry building society offer some of the best cash ISA rates, but the products are time limited so you have to get in quick.
I’d go for a mix of premium bonds, cash ISA, and stocks & shares ISA for tax free saving.