Finding appropriate sportswear for hijab is really challenging, especially as it starts to get warmer. (Islamic clothing companies, take note...) Whilst it's easy enough to find baggy bottoms, in all honesty I've yet to find a top I'm comfortable enough in when sweating it out in the gym. What would be ideal is a simple cotton long sleeved tunic that is loose in the body but a little more fitted in the sleeves.
Shukr though does have this Maliki hoodie (£34.95) which might be an option, espcially if you like to exercise outside. I'd wear only a thin vest top underneath to avoid overheating. Then just add jogging bottoms, and one-piece cotton Al-amirah, trainers, and you're all set: