Hi Noquarter,
While I don’t recommend specific mattresses for people because only your own experience can tell you whether a mattress is a suitable choice in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences) … Brooklyn Bedding and Dreamfoam (which is one of their brands) are members of this site which means that I believe they are among the best quality and value in the country and they are certainly a recommended choice.
Both of the mattresses you are considering use good quality materials and have good value although they are also different (the Ultimate Dreams is a latex/polyfoam hybrid and the Ikea is an all latex mattress) but if you are comfortable with an online purchase that you can’t test before a purchase then the people at Dreamfoam do a good job of providing information that can help their customers make suitable choices and they are certainly a great choice in terms of quality and value as well.
Phoenix