FWIW - if your affairs are simple then if you need to claim additional relief on your pension contributions then you can do this without a self assessment, you can phone up HMRC or get setup with a personal tax account and send them a message, they'll either refund you if it's a fair bit or adjust your tax code.
Found myself in a similar position towards the end of the last tax year so opened up a vanguard account and setup a pension in there so I can easily make additional payments to keep under the all important tax bracket. Now I've got that sorted I've finally got a S&S Isa in place to build up a couple of years of cash when I retire in case the market tanks near retirement so I can take money out my pension at the right time.
Found myself in a similar position towards the end of the last tax year so opened up a vanguard account and setup a pension in there so I can easily make additional payments to keep under the all important tax bracket. Now I've got that sorted I've finally got a S&S Isa in place to build up a couple of years of cash when I retire in case the market tanks near retirement so I can take money out my pension at the right time.