Where I'm unsure, is that you have used the term Director in your thread title and Sole Trader in your post. I'm a Ltd Co. proprietary director and don't know how it works for Sole Traders.
There are complicated rules around the level of contribution your company can make to an Executive Pension plan relative to your salary from the company. The rules involve details of your length of service with the company, existing pension funds from other sources, retirement age, marital status etc.
There are also rules around maximum contributions for dual income scenarios like yours.
A sole trader and a company director are two very different things for taxation and pension planning purposes.
An execution only service is intended for people who don't need any advice. I suspect that you do need professional advice as what you're proposing to do requires you to understand the rules of both contributions to Executive Pension plans, PRSAs and how they interact with each other in a dual income scenario.
That said, it is permissible for you to have both.