Not short of a fence that wouldn't be very attractive. Like all plants, they grow in the direction and manner that provides the most sun to their foliage.

Lavenders come in a range of sizes and the smaller cultivars tend to be more upright. Also, unless they are cut back each season, they will tend to splay or flop.

Do they look healthy? I’m not sure if they’re flopping bc the stems are heavy or they need more water

It's just their nature. And likely too rich a growing environment. Lavender likes it lean and mean.