@jojoe Hi jojoe!!
I have also what you refer to as "ice plant" (Lampranthus blandus) and from what I have seen so far, this plant is rigid, grows straight up and out (some branching) and can crowd out anything that is small and close to the soil. The crassula will grow up and when the branch gets tall enough, it may arch a little but something low can be grown underneath.
My method for chosing companions for already chosen foundation plants (your ice plant and your crassula) is to have an inventory of different plants sitting alongside your oval pot as you decide what to plant. Then just place each one into the pot temporarily to see if color or texture compliments the two foundation plants. Recommendations can be made galore but it's really what you find pleasant to look at in your pot and what
you think goes that is most important. Of course, take into consideration plants with similar needs as your chosen foundation plants.
Since these two plants grow up and one does grow sideways too (the Lampranthus), I would try to have on hand some plants that are roundish or rosette in shape to balance the tallness of your plants. When you find you have your base plants chosen that give structure to your planting, then look for softer, flowing, clustering, or spreading plants on top of soil to fill in the empty spaces below the tall plants.
Here's some plantings I've done to illustrate my points. Hope some of this helps. If anything, it may help you to decide what you don't want. Remember, it is most important to choose plants with similar needs so that the planting can be treated as one unit to maintain.
This was really a collection of echeveria and what could go with them to add more color and texture. I wanted the full look right away for 'instant gratification':
Here's a planting that started with the senecio as the focus plant and what I could squeeze in with it to have a backdrop and then something that would contrast with its long spindley arms, so I added a sedum clavatum with its chubby leaves and rounded edges, but also a kalanchoe with its rounded leaves but delicate stems.
This is the first planting with Lampranthus
