Got hayfever and dust mite allergies myself and family, tried the mieles and panasonics and other high end vacs with hepa filters, yes they are more powerful due to being corded the hepa filters are large so should capture a lot of dust but I can't use an Miele or corded vac, once you use a cordless Dyson you can't go back you can literally clean in a fraction of the time it takes a corded vac.
Also most top end dysons also have hepa filters like v8 absolute and others, I empty mine out on my daily runs and don't sneeze or have issue.
I would also invest in some decent dust mite spray and spray beds, mattresses and pillows or get dust mite protector sheets. You can also vac the bedding for
dust ( I use my dyson v8 and always find some dust!) you can use essential oils mixed together or tree tea oil, lemon etc. Wash all clothes, bedding @ 60 degree etc
Choice is yours maybe check the vacs websites some may offer a 30 day trial peroid, dyson have currently, but I would keep an eye out on the dyson ebay
refurb store, lots of bargains at times.