For custodial, River or Strike can serve this purpose better than Coinbase. You don't have to leave funds with the custodian for long but can instead use them as a pretty seamless "swap" service to get in/out of Lightning.

For non-custodial, Aqua is probably the simplest. Requires a couple steps because you have to peg in or out between Liquid <> on-chain BTC. Funds at rest are L-BTC, but you can pay Lightning invoices, which happen via a Boltz swap under the hood.

Blockstream's Green wallet also makes it pretty easy to receive on-chain BTC to automatically open new channels and enable LN payments.