If buying from exchanges that don't offer Lighting withdrawals you can use Boltz for a swap (0.1% swap fee) or Sideswap's website to perform a peg-in (0.1% swap fee).

https://sideswap.io/peg-in-out/

They also have an app if you prefer.

Depending on the amount it might take 2 or 102 confirmations. Check their FAQ for details.

Tdex is another app that let you peg-in (0.0%). It takes 102 confirmations.

If you use an exchange (Robosats, Relai coming soon) that do LN withdraws, you can use Boltz to swap into Liquid (0.25% swap fee).

For peg-out to Bitcoin, you can use Boltz (0.5% swap fee) or SideSwap website or app (0.1% pet-out fee).